Network B. Welch Internet-Draft B. Halevy Expires: January 16, 2006 Panasas G. Goodson NetApp D. Black EMC A. Adamson CITI July 15, 2005 pNFS Operations draft-welch-pnfs-ops-03.txt Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on January 16, 2006. Copyright Notice Copyright (C) The Internet Society (2005). Abstract This Internet-Draft provides a description of the pNFS extension for NFSv4. Welch, et al. Expires January 16, 2006 [Page 1] Internet-Draft pNFS Operations July 2005 The key feature of the protocol extension is the ability for clients to perform read and write operations that go directly from the client to individual storage system elements without funneling all such accesses through a single file server. Of course, the file server must provide sufficient coordination of the client I/O so that the file system retains its integrity. The extension adds operations that query and manage layout information that allows parallel I/O between clients and storage system elements. The layouts are managed in a similar way to delegations in that they are associated with leases and can be recalled by the server, but layout information is independent of delegations. Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [1]. Welch, et al. Expires January 16, 2006 [Page 2] Internet-Draft pNFS Operations July 2005 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 6 2. General Definitions . . . . . . . . . . . . . . . . . . . . . 8 2.1 Metadata Server . . . . . . . . . . . . . . . . . . . . . 8 2.2 Client . . . . . . . . . . . . . . . . . . . . . . . . . . 8 2.3 Storage Device . . . . . . . . . . . . . . . . . . . . . . 8 2.4 Storage Protocol . . . . . . . . . . . . . . . . . . . . . 9 2.5 Management Protocol . . . . . . . . . . . . . . . . . . . 9 2.6 Metadata . . . . . . . . . . . . . . . . . . . . . . . . . 9 2.7 Layout . . . . . . . . . . . . . . . . . . . . . . . . . . 10 3. Layouts and Aggregation . . . . . . . . . . . . . . . . . . . 10 3.1 Layout Structure . . . . . . . . . . . . . . . . . . . . . 10 3.1.1 Device IDs . . . . . . . . . . . . . . . . . . . . . . 11 3.1.2 Aggregation Schemes . . . . . . . . . . . . . . . . . 11 3.2 Basic Layout Semantics . . . . . . . . . . . . . . . . . . 12 3.2.1 Layouts and access control . . . . . . . . . . . . . . 12 3.2.2 Layout Iomode . . . . . . . . . . . . . . . . . . . . 13 3.2.3 Operation Sequencing . . . . . . . . . . . . . . . . . 13 3.3 Obtaining a Layout . . . . . . . . . . . . . . . . . . . . 14 3.3.1 Identifying Layouts . . . . . . . . . . . . . . . . . 14 3.3.2 Overlapping Layouts . . . . . . . . . . . . . . . . . 15 3.3.3 Copy-on-write . . . . . . . . . . . . . . . . . . . . 15 3.4 Recalling a Layout . . . . . . . . . . . . . . . . . . . . 15 3.5 Committing a Layout . . . . . . . . . . . . . . . . . . . 16 3.5.1 LAYOUTCOMMIT and mtime/atime/change . . . . . . . . . 17 3.5.2 LAYOUTCOMMIT and size . . . . . . . . . . . . . . . . 18 3.5.3 LAYOUTCOMMIT and layoutupdate . . . . . . . . . . . . 19 3.6 Crash Recovery . . . . . . . . . . . . . . . . . . . . . . 19 3.6.1 Leases . . . . . . . . . . . . . . . . . . . . . . . . 19 3.6.2 Client Recovery . . . . . . . . . . . . . . . . . . . 21 3.6.3 Metadata Server Recovery . . . . . . . . . . . . . . . 21 4. Security Considerations . . . . . . . . . . . . . . . . . . . 23 4.1 File Layout Security . . . . . . . . . . . . . . . . . . . 24 4.2 Object Layout Security . . . . . . . . . . . . . . . . . . 24 4.3 Block Layout Security . . . . . . . . . . . . . . . . . . 25 5. NFSv4 File Layout Type . . . . . . . . . . . . . . . . . . . . 26 5.1 File Striping and Data Access . . . . . . . . . . . . . . 26 5.1.1 Sparse and Dense Storage Device Data Layouts . . . . . 28 5.1.2 Operations Issued to Storage Devices . . . . . . . . . 29 5.2 Global Stateid Requirements . . . . . . . . . . . . . . . 30 5.3 The Layout Iomode . . . . . . . . . . . . . . . . . . . . 30 5.4 Storage Device State Propagation . . . . . . . . . . . . . 31 5.4.1 Lock State Propagation . . . . . . . . . . . . . . . . 31 5.4.2 Open-mode Validation . . . . . . . . . . . . . . . . . 32 5.4.3 File Attributes . . . . . . . . . . . . . . . . . . . 32 5.5 Extending file size . . . . . . . . . . . . . . . . . . . 33 5.5.1 READs and EOF . . . . . . . . . . . . . . . . . . . . 33 Welch, et al. Expires January 16, 2006 [Page 3] Internet-Draft pNFS Operations July 2005 5.5.2 LAYOUTCOMMIT and EOF . . . . . . . . . . . . . . . . . 33 5.6 Crash Recovery Considerations . . . . . . . . . . . . . . 34 5.7 Security Considerations . . . . . . . . . . . . . . . . . 35 5.8 Alternate Approaches . . . . . . . . . . . . . . . . . . . 35 6. pNFS Typed Data Structures . . . . . . . . . . . . . . . . . . 36 6.1 pnfs_layouttype4 . . . . . . . . . . . . . . . . . . . . . 36 6.2 pnfs_deviceid4 . . . . . . . . . . . . . . . . . . . . . . 36 6.3 pnfs_devaddr4 . . . . . . . . . . . . . . . . . . . . . . 37 6.4 pnfs_devlist_item4 . . . . . . . . . . . . . . . . . . . . 37 6.5 pnfs_layout4 . . . . . . . . . . . . . . . . . . . . . . . 37 6.6 pnfs_layoutupdate4 . . . . . . . . . . . . . . . . . . . . 38 6.7 pnfs_layoutiomode4 . . . . . . . . . . . . . . . . . . . . 38 7. pNFS File Attributes . . . . . . . . . . . . . . . . . . . . . 38 7.1 pnfs_layouttype4<> FS_LAYOUT_TYPES . . . . . . . . . . . . 39 7.2 pnfs_layouttype4<> FILE_LAYOUT_TYPE . . . . . . . . . . . 39 7.3 pnfs_layouttypes4 FILE_LAYOUT_HINT . . . . . . . . . . . . 39 7.4 uint32_t FS_LAYOUT_PREFERRED_BLOCKSIZE . . . . . . . . . . 39 7.5 uint32_t FS_LAYOUT_PREFERRED_ALIGNMENT . . . . . . . . . . 39 8. pNFS Error Definitions . . . . . . . . . . . . . . . . . . . . 39 9. pNFS Operations . . . . . . . . . . . . . . . . . . . . . . . 40 9.1 LAYOUTGET - Get Layout Information . . . . . . . . . . . . 40 9.2 LAYOUTCOMMIT - Commit writes made using a layout . . . . . 42 9.3 LAYOUTRETURN - Release Layout Information . . . . . . . . 46 9.4 GETDEVICEINFO - Get Device Information . . . . . . . . . . 47 9.5 GETDEVICELIST - Get List of Devices . . . . . . . . . . . 49 10. Callback Operations . . . . . . . . . . . . . . . . . . . . 50 10.1 CB_LAYOUTRECALL . . . . . . . . . . . . . . . . . . . . . 50 10.2 CB_SIZECHANGED . . . . . . . . . . . . . . . . . . . . . . 52 11. Usage Scenarios . . . . . . . . . . . . . . . . . . . . . . 52 11.1 Basic Read Scenario . . . . . . . . . . . . . . . . . . . 53 11.2 Multiple Reads to a File . . . . . . . . . . . . . . . . . 53 11.3 Multiple Reads to a File with Delegations . . . . . . . . 53 11.4 Read with existing writers . . . . . . . . . . . . . . . . 53 11.5 Read with later conflict . . . . . . . . . . . . . . . . . 54 11.6 Basic Write Case . . . . . . . . . . . . . . . . . . . . . 54 11.7 Large Write Case . . . . . . . . . . . . . . . . . . . . . 55 11.8 Create with special layout . . . . . . . . . . . . . . . . 55 12. Layouts and Aggregation . . . . . . . . . . . . . . . . . . 55 12.1 Simple Map . . . . . . . . . . . . . . . . . . . . . . . . 55 12.2 Block Map . . . . . . . . . . . . . . . . . . . . . . . . 55 12.3 Striped Map (RAID 0) . . . . . . . . . . . . . . . . . . . 56 12.4 Replicated Map . . . . . . . . . . . . . . . . . . . . . . 56 12.5 Concatenated Map . . . . . . . . . . . . . . . . . . . . . 56 12.6 Nested Map . . . . . . . . . . . . . . . . . . . . . . . . 56 13. Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 13.1 Storage Protocol Negotiation . . . . . . . . . . . . . . . 57 13.2 Storage Errors . . . . . . . . . . . . . . . . . . . . . . 57 14. Normative References . . . . . . . . . . . . . . . . . . . . 57 Welch, et al. Expires January 16, 2006 [Page 4] Internet-Draft pNFS Operations July 2005 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 57 A. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 58 Intellectual Property and Copyright Statements . . . . . . . . 59 Welch, et al. Expires January 16, 2006 [Page 5] Internet-Draft pNFS Operations July 2005 1. Introduction The NFSv4 protocol [2] specifies the interaction between a client that accesses files and a server that provides access to files and is responsible for coordinating access by multiple clients. As described in the pNFS problem statement, this requires that all access to a set of files exported by a single NFSv4 server be performed by that server; at high data rates the server may become a bottleneck. The parallel NFS (pNFS) extensions to NFSv4 allow data accesses to bypass this bottleneck by permitting direct client access to the storage devices containing the file data. When file data for a single NFSv4 server is stored on multiple and/or higher throughput storage devices (by comparison to the server's throughput capability), the result can be significantly better file access performance. The relationship among multiple clients, a single server, and multiple storage devices for pNFS (server and clients have access to all storage devices) is shown in this diagram: +-----------+ |+-----------+ +-----------+ ||+-----------+ | | ||| | NFSv4 + pNFS | | +|| Clients |<------------------------------>| Server | +| | | | +-----------+ | | ||| +-----------+ ||| | ||| | ||| Storage +-----------+ | ||| Protocol |+-----------+ | ||+----------------||+-----------+ Management| |+-----------------||| | Protocol| +------------------+|| Storage |------------+ +| Devices | +-----------+ Figure 1 In this structure, the responsibility for coordination of file access by multiple clients is shared among the server, clients, and storage devices. This is in contrast to NFSv4 without pNFS extensions, in which this is primarily the server's responsibility, some of which can be delegated to clients under strictly specified conditions. The pNFS extension to NFSv4 takes the form of new operations that manage data location information called a "layout". The layout is Welch, et al. Expires January 16, 2006 [Page 6] Internet-Draft pNFS Operations July 2005 managed in a similar fashion as NFSv4 data delegations (e.g., they are recallable and revocable). However, they are distinct abstractions and are manipulated with new operations that are described in Section 9. When a client holds a layout, it has rights to access the data directly using the location information in the layout. There are new attributes that describe general layout characteristics. However, much of the required information cannot be managed solely within the attribute framework, because it will need to have a strictly limited term of validity, subject to invalidation by the server. This requires the use of new operations to obtain, return, recall, and modify layouts, in addition to new attributes. This document specifies both the NFSv4 extensions required to distribute file access coordination between the server and its clients and a NFSv4 file storage protocol that may be used to access data stored on NFSv4 storage devices. Storage protocols used to access a variety of other storage devices are deliberately not specified here. These might include: o Block protocols such as iSCSI, parallel SCSI, and FCP (SCSI over Fibre Channel) [refs]. The block protocol support can be independent of the addressing structure of the block protocol used, allowing more than one protocol to access the same file data and enabling extensibility to other block protocols. o Object protocols such as OSD over iSCSI or Fibre Channel [3]. o Other storage protocols, including PVFS and other file systems that are in use in HPC environments. pNFS is designed to accommodate these protocols and be extensible to new classes of storage protocols that may be of interest. The distribution of file access coordination between the server and its clients increases the level of responsibility placed on clients. Clients are already responsible for ensuring that suitable access checks are made to cached data and that attributes are suitably propagated to the server. Generally, a misbehaving client that hosts only a single-user can only impact files accessible to that single user. Misbehavior by a client hosting multiple users may impact files accessible to all of its users. NFSv4 delegations increase the level of client responsibility as a client that carries out actions requiring a delegation without obtaining that delegation will cause its user(s) to see unexpected and/or incorrect behavior. Welch, et al. Expires January 16, 2006 [Page 7] Internet-Draft pNFS Operations July 2005 Some uses of pNFS extend the responsibility of clients beyond delegations. In some configurations, the storage devices cannot perform fine-grained access checks to ensure that clients are only performing accesses within the bounds permitted to them by the pNFS operations with the server (e.g., the checks may only be possible at file system granularity rather than file granularity). In situations where this added responsibility placed on clients creates unacceptable security risks, pNFS configurations in which storage devices cannot perform fine-grained access checks SHOULD NOT be used. All pNFS server implementations MUST support NFSv4 access to any file accessible via pNFS in order to provide an interoperable means of file access in such situations. See Section 4 on Security for further discussion. Finally, there are issues about how layouts interact with the existing NFSv4 abstractions of data delegations and byte range locking. These issues (and more) are also discussed here. 2. General Definitions This protocol extension partitions the NFSv4 file system protocol into two parts, the control path and the data path. The control path is implemented by the extended (p)NFSv4 server. When the file system being exported by (p)NFSv4 uses storage devices that are visible to clients over the network, the data path may be implemented by direct communication between the extended (p)NFSv4 file system client and the storage devices. This leads to a few new terms used to describe the protocol extension and some clarifications of existing terms. 2.1 Metadata Server A pNFS "server" or "metadata server" is a server as defined by RFC3530 [2], which additionally provides support of the pNFS minor extension. When using the pNFS NFSv4 minor extension, the metadata server may hold only the metadata associated with a file, while the data is stored on the storage devices. Note: directory data is always accessed through the metadata server. 2.2 Client A pNFS "client" is a client as defined by RFC3530 [2], with the addition of supporting the pNFS minor extension server protocol and with the addition of supporting at least one storage protocol (for performing I/O directly to storage devices). 2.3 Storage Device This is a device, or server, that controls the file's data, but Welch, et al. Expires January 16, 2006 [Page 8] Internet-Draft pNFS Operations July 2005 leaves other metadata management up to the metadata server. A storage device could be another NFS server, or an Object Storage Device (OSD) or a block device accessed over a SAN (either FiberChannel or iSCSI SAN). The goal of this extension is to allow direct communication between clients and storage devices. 2.4 Storage Protocol This is the protocol between the pNFS client and the storage device used to access the file data. Three following types have been described: file protocols (such as NFSv4 or NFSv3), object protocols (OSD), and block protocols (SCSI-block commands, or "SBC"). These protocols are in turn layered over transport protocols such as RPC/ TCP/IP or iSCSI/TCP/IP or FC/SCSI. We anticipate there will be variations on these storage protocols, including new protocols that are unknown at this time or experimental in nature. The details of the storage protocols will be described in other documents so that pNFS clients can be written to use these storage protocols. Use of NFSv4 itself as a file-based storage protocol is described in Section 5. 2.5 Management Protocol This is a protocol used by the exported file system between the server and storage devices. Specification of such protocols is outside the scope of this draft. Such management protocols would be used to control such activities as the allocation and deallocation of storage and the management of state required by the storage devices to perform client access control. The management protocol should not be confused with protocols used to manage LUNs in a SAN and other sysadmin kinds of tasks. While the pNFS protocol allows for any management protocol, in practice the management protocol is closely related to the storage protocol. For example, if the storage devices are NFS servers, then the protocol between the pNFS metadata server and the storage devices is likely to involve NFS operations. Similarly, when object storage devices are used, the pNFS metadata server will likely use iSCSI/OSD commands to manipulate storage. However, this document does not mandate any particular management protocol. Instead, it just describes the requirements on the management protocol for maintaining attributes like modify time, the change attribute, and the end-of-file position. 2.6 Metadata This is information about a file, like its name, owner, where it Welch, et al. Expires January 16, 2006 [Page 9] Internet-Draft pNFS Operations July 2005 stored, and so forth. The information is managed by the exported file system server (metadata server). Metadata also includes lower- level information like block addresses and indirect block pointers. Depending the storage protocol, block-level metadata may or may not be managed by the metadata server, but is instead managed by Object Storage Devices or other servers acting as a storage device. 2.7 Layout A layout defines how a file's data is organized on one or more storage devices. There are many possible layout types. They vary in the storage protocol used to access the data, and in the aggregation scheme that lays out the file data on the underlying storage devices. Layouts are described in more detail below. 3. Layouts and Aggregation 3.1 Layout Structure The layout is a typed data structure that has variants to handle different storage protocols (block, object, and file). A layout describes a range of a file's contents (e.g., the set of storage devices on which a specific byte range of the file's data reside and a method for identifying the data on those devices). A specific layout structure belongs to a "layout type" (e.g., blocks, objects, files). A metadata server, along with its management protocol, must support at least one layout type. See Section 6.1 for the RPC definition of a layout type. A private sub-range of the layout type name space can be defined (e.g., a type with the high bit set to one). This private sub-range can be used for internal testing or experimentation. For example, a file layout type could be an array of tuples (deviceID, file_handle), along with a definition (or aggregation scheme) of how the data is stored across the devices (e.g., striping). A block layout might be an array of tuples that store (deviceID, block_number, block count) along with information about block size and the file offset of the first block. An object layout is an array of tuples (deviceID, objectID) and an additional structure (i.e., the aggregation map) that defines how the logical byte sequence of the file data is serialized into the different objects. This document defines a NFSv4 file layout type using a stripe-based aggregation scheme (see Section 5). Adjunct specifications must exist that precisely define other layout formats (e.g., blocks, objects, or other file-based layouts) to allow interoperability among clients and metadata servers. Welch, et al. Expires January 16, 2006 [Page 10] Internet-Draft pNFS Operations July 2005 3.1.1 Device IDs The "deviceID" is a short name for a storage device. In practice, a significant amount of information may be required to fully identify a storage device. Instead of embedding all that information in a layout, a level of indirection is used. Layouts embed device IDs, and a new op (GETDEVICEINFO) is used to retrieve the complete identity information about the storage device (according to its layout type). For example, the identity of a file server or object server could be an IP address and port. The identity of a block device could be a volume label. Due to multipath connectivity in a SAN environment, agreement on a volume label is considered the reliable way to locate a particular storage device. The device ID is qualified by the layout type. This allows different layout drivers to generate device IDs without the need for co- ordination. In addition to GETDEVICEINFO, another operation, GETDEVICELIST, has been added to allow clients to fetch the mappings of multiple storage devices attached to a metadata server. Clients SHOULD NOT expect the mapping between device ID and storage device address to exist across metadata server reboots (i.e., clients should fetch new mappings upon startup or upon detection of a metadata server reboot). If data are reorganized from a storage device with a given device ID to a different storage device (i.e., if the mapping between storage device and data changes), the layout describing the data MUST be recalled rather than assigning the new storage device to the old device ID. [OPEN ISSUE: we could associate leases with device IDs; this seems overly complex. As well, we could introduce an invalidation process, instead of recalling layouts if mapping changes; again seems overly complex.] 3.1.2 Aggregation Schemes Aggregation schemes can describe layouts like simple one-to-one mapping, concatenation, and striping. A general aggregation scheme allows nested maps so that more complex layouts can be compactly described. The canonical aggregation type for this extension is striping, which allows a client to access storage devices in parallel. Even a one-to-one mapping is useful for a file server that wishes to distribute its load among a set of other file servers. There are also experimental aggregation types such as writable mirrors and client-implemented RAID that could be defined. [OPEN ISSUE: should aggregation schemes (striping) be moved up a level and made not opaque. I.e., there would exist a generic Welch, et al. Expires January 16, 2006 [Page 11] Internet-Draft pNFS Operations July 2005 striping mechanisms that could be shared by file/block/object specifications.] 3.2 Basic Layout Semantics Layouts delegate to the client the ability to access data out of band. The layout guarantees the holder that the layout will be recalled when the state encapsulated by the layout becomes invalid (e.g., through some operation that directly or indirectly modifies the layout) or, possibly, when a conflicting layout is requested, as determined by the layout's iomode. When a layout is recalled, and then returned by the client, the client retains the ability to access file data with normal NFSv4 I/O operations through the metadata server. Only the right to do I/O out-of-band is affected. 3.2.1 Layouts and access control Holding a layout does not guarantee that a user of the layout has the rights to access the data represented by the layout. All user access rights MUST be obtained through the appropriate open, lock, and access operations. However, if a valid layout for a file is not held by the client, the storage device will reject all I/Os to that file's byte range that originate from that client. In summary, layouts and ordinary file access controls are independent. The act of modifying a file for which a layout is held, does not necessarily conflict with the holding of the layout (that describes the file being modified). However, with certain layout types (e.g., block layouts), the layout's iomode must agree with the type of I/O being performed. Depending upon the layout type and storage protocol in use, storage device access permissions may be granted by LAYOUTGET and may be encoded within the type specific layout. If access permissions are encoded within the layout, the metadata server should recall the layout when the file's ACL or mode changes. For example, the object layout protocol encodes access permissions within the capability embedded within the layout; if these permissions change, the layout is recalled and the capability revoked. Note, clients are still required to perform the appropriate access operations as described above (e.g., open and lock ops). The degree to which it is possible for the client to circumvent these access operations must be clearly addressed by the individual layout type documents, as well as the consequences of doing so. In addition, these documents must be clear about the requirements and non-requirements for the checking performed by the server. If the pNFS metadata server supports mandatory byte range locks then byte range locks must behave as specified by the NFSv4 protocol (as seen by users of files). If a storage device is unable to restrict Welch, et al. Expires January 16, 2006 [Page 12] Internet-Draft pNFS Operations July 2005 access by a pNFS client who does not hold a required mandatory byte range lock then the metadata server must not grant layouts to a client, for that storage device, that permits any access that conflicts with a mandatory byte range lock held by another client. In this scenario, it is also necessary for the metadata server to ensure that byte range locks are not granted to a client if any other client holds a conflicting layout; in this case all conflicting layouts must be recalled and returned before the lock request can be granted. This requires the pNFS server to understand the capabilities of its storage devices. 3.2.2 Layout Iomode When requesting a layout (through LAYOUTGET), the client MUST request a layout pertaining to an "iomode" of either READ or READ/WRITE. The iomode indicates to the metadata server the client's intent to perform either READs (only) or a mixture of I/O possibly containing WRITEs as well (READ/WRITE). For certain layout types, it is useful for a client to specify this intent at LAYOUTGET time. E.g., for block based protocols, block allocation could occur when a READ/WRITE iomode is specified. A storage device may validate I/O with regards to the iomode; this is dependent upon storage device implementation. Thus, if the client's layout iomode differs from the I/O being performed the storage device may reject the client's I/O with an error indicating a new layout with the correct I/O mode should be fetched. E.g., if a client gets a layout with a READ iomode and performs a WRITE to a storage device, the storage device is allowed to reject that WRITE. The iomode does not conflict with OPEN share modes or lock requests, and these are the preferred method for restricting user access to data files. E.g., an OPEN of read, deny-write does not conflict with a LAYOUTGET containing an iomode of READ/WRITE performed by another client. Applications that depend on writing into the same file concurrently may use byte range locking to serialize their accesses. 3.2.3 Operation Sequencing As with other stateful operations, pNFS requires the correct sequencing of layout operations. This proposal assumes that sessions will precede pNFS into NFSv4.x and thus, pNFS will require the use of sessions. If the sessions proposal does not precede pNFS, then this proposal needs to be modified to provide for the correct sequencing of pNFS layout operations. It is the server's responsibility to avoid inconsistencies regarding the layouts it hands out. One critical issue with operation sequencing concerns callbacks. The protocol must defend against races between the reply to a LAYOUTGET Welch, et al. Expires January 16, 2006 [Page 13] Internet-Draft pNFS Operations July 2005 operation and a subsequent CB_LAYOUTRECALL. It MUST NOT be possible for a client to process the CB_LAYOUTRECALL for a layout that it has not received in a reply message to a LAYOUTGET. [OPEN ISSUE: the mechanism for doing this is still an open issue. It may be sufficient to add a seqid to LAYOUTGET/LAYOUTRETURN.] 3.3 Obtaining a Layout The metadata server will give out layouts of a particular type (block, object, or file) and aggregation as requested by the client. A client obtains a layout through a new operation (LAYOUTGET). The client selects an appropriate layout type which the server supports and the client is prepared to use. The layout returned to the client may not line up exactly with the requested byte range. However, at least a single byte overlap MUST exist between the requested layout and the layout returned by the metadata server. There is no implied ordering between getting a layout and performing a file OPEN. For example, a layout may first be retrieved by placing a LAYOUTGET operation in the same compound as the initial file OPEN. Once the layout has been retrieved, it can be held across multiple OPEN and CLOSE sequences. The storage protocol used by the client to access the data on the storage device is determined by the layout's type. The client needs to select a "layout driver" that understands how to interpret and use that layout. The API used by the client to talk to its drivers is outside the scope of the pNFS extension. The storage protocol between the client's layout driver and the actual storage is covered by other protocols specifications such as SBC (block storage), OSD (object storage) or NFS (file storage). Although, the metadata server is in control of the layout for a file, the pNFS client can provide hints to the server when a file is opened or created about preferred layout type and aggregation scheme. The pNFS extension introduces a LAYOUT_HINT attribute that the client can set at creation time to provide a hint to the server for new files. It is suggested that this attribute be set as one of the initial attributes to OPEN when creating a new file. Setting this attribute separately, after the file has been created could make it difficult (or impossible) for the server implementation to comply. 3.3.1 Identifying Layouts A layout is identified by the following tuple: (ClientID, FH, offset, length, layout type, iomode); the FH refers to the FH of the file on the metadata server, the offset and length specify the byte range of Welch, et al. Expires January 16, 2006 [Page 14] Internet-Draft pNFS Operations July 2005 the file covered by the layout. The iomode specifies the client's intent for data access (as described previously). Including the iomode in the layout allows for distinct read-only and writable (and readable) layouts to be held, possibly simultaneously (depending on the layout type specific protocol). Since there is a desire to manage layouts as sub-dividable entities, layouts are range-based and are identified in such a manner. Sub- dividable layouts have the benefit of being returnable/recallable or committable in smaller chunks without having to return, recall, or commit the entire layout. E.g., this may be useful when the layout is very large and a client is only actively using a small range of the layout, thus the client may not want to commit the entire layout, rather it could commit just the range of the layout it is using. 3.3.2 Overlapping Layouts A metadata server may hand-out layouts, to the same client, that overlap, as long as the overlapping regions specify the same storage device/file mapping; i.e., the records within the overlapping layouts should specify the same storage device mapping for the same byte ranges they represent. If two overlapping layouts, of the same type and iomode, differ, the old layout should be recalled and returned, before giving out the new layout. 3.3.3 Copy-on-write [OPEN ISSUE] For block-based protocols, it is useful to have the ability to direct a client to read data from one group of blocks, but write to a different group; e.g., to implement a snapshotting blocks system. The client cannot make the choice of where to place data, it requires help from the metadata server, most probably communicated through the layout. A single layout with the ability to mark (and re-mark) portions read-only vs. read/write is sufficient for this to work. Alternatively, separate read-only vs. read/write layouts, as identified by the iomode, may be given out. 3.4 Recalling a Layout Since a layout protects a client's access to a file via a direct client-data-server path, a layout need only be recalled when it is semantically unable to serve this function. Typically, this occurs when the layout no longer encapsulates the true location of the file over the byte range it represents. Any operation or action (e.g., server driven restriping or load balancing) that changes the layout will result in a recall of the layout. A layout is recalled by the Welch, et al. Expires January 16, 2006 [Page 15] Internet-Draft pNFS Operations July 2005 CB_LAYOUTRECALL callback operation (see Section 10.1). This callback can either recall a layout identified by a byte range, or all the layouts associated with a file system (FSID). The iomode must also be specified when recalling layouts. A special LAYOUTIOMODE_ANY enumeration is defined to enable recalling a layout of any type (i.e., the client must return both read-only and read/write layouts). A REMOVE operation may cause the metadata server to recall the layout to prevent the client from accessing a non-existent file and to reclaim state stored on the client. Since a REMOVE may be delayed until the last close of the file has occurred, the recall may also be delayed until this time. As well, once the file has been removed (after the last reference), the client SHOULD no longer be able to perform I/O using the layout (e.g., with file-based layouts an error such as ESTALE could be returned). Although, the pNFS extension does not alter the caching capabilities of clients (or their semantics) it recognizes that some clients may perform more aggressive write-behind caching to optimize the benefits provided by pNFS. However, write-behind caching may impact the latency in returning a layout in response to a CB_LAYOUTRECALL; just as caching impacts DELEGRETURN with regards to data delegations. Client implementations should limit the amount of dirty data they have outstanding at any one time. Server implementations may fence clients from performing direct I/O to the storage devices if they perceive that the client is taking too long to return a layout once recalled. A server may be able to monitor client progress by watching client I/Os or by observing LAYOUTRETURNs of sub-portions of the recalled layout. The server can also limit the amount of dirty data to be flushed to storage devices by limiting the byte ranges covered in the layouts it gives out. Once a layout has been returned, the client should no longer issue I/Os to the storage devices for the file, byte range, and iomode represented by the returned layout. If a client does issue an I/O to a storage device for which it does not hold a layout, the storage device may reject the I/O. 3.5 Committing a Layout Due to the nature of the protocol, the file attributes that exist on the metadata storage device may become inconsistent in relation to the data stored on the storage devices; e.g., when WRITEs occur before a layout has been committed (e.g., between a LAYOUTGET and a LAYOUTCOMMIT). Thus, it is necessary to occasionally re-sync this state and make it visible to other clients through the metadata server. Welch, et al. Expires January 16, 2006 [Page 16] Internet-Draft pNFS Operations July 2005 The LAYOUTCOMMIT operation is responsible for committing the modified layout to the metadata server. Note: the data should be written (and committed) to the appropriate storage devices before the LAYOUTCOMMIT occurs. The scope of this operation depends on the storage protocol in use. For block-based layouts, it may require updating the block list that comprises the file and committing this layout to stable storage. While, for file-layouts it requires some synchronization of attributes between the metadata and storage devices (mainly the size attribute; EOF). It is important to note that the level of synchronization is from the point of view of the client who issued the LAYOUTCOMMIT. The updated state on the metadata server need only reflect the state as of the client's last operation (previous to the LAYOUTCOMMIT), it need not reflect a globally synchronized state (e.g., other clients may be performing, or may have performed I/O since the client's last operation and the LAYOUTCOMMIT). The management protocol is free to synchronize the attributes before it receives a LAYOUTCOMMIT, however upon successful completion of a LAYOUTCOMMIT, state that exists on the metadata server that describes the file MUST be in sync with the state existing on the storage devices that comprise that file as of the issuing client's last operation. Thus, a client that queries the size of a file between a WRITE to a storage device and the LAYOUTCOMMIT may observe a size that does not reflects the actual data written. 3.5.1 LAYOUTCOMMIT and mtime/atime/change The change attribute and the modify/access times may be updated, by the server, at LAYOUTCOMMIT time; since for some layout types, the change attribute (and atime/mtime) can not be updated by the appropriate I/O operation performed at a storage device. The arguments to LAYOUTCOMMIT allow the client to provide suggested access and modify time values to the server. Again, depending upon the layout type, these client provided values may or may not be used. The server should sanity check the client provided values before they are used. For example, the server should ensure that time does not flow backwards. The client always has the option to set these attributes (according to the NFSv4 specification) through an explicit SETATTR operation. As mentioned, for some layout protocols the change attribute and mtime/atime may be updated at or after the time the I/O occurred (e.g., if the storage device is able to communicate these attributes to the metadata server). If, upon receiving a LAYOUTCOMMIT, the server implementation is able to determine that the file did not change since the last time the change attribute was updated (e.g., no WRITEs or over-writes occurred), the implementation need not update the change attribute (file-based protocols may have enough state to Welch, et al. Expires January 16, 2006 [Page 17] Internet-Draft pNFS Operations July 2005 make this determination or may update the change attribute upon each file modification). This also applies for mtime and atime; if the server implementation is able to determine that the file has not been modified since the last mtime update, the server need not update mtime at LAYOUTCOMMIT time. Once LAYOUTCOMMIT completes, the new change attribute and mtime/atime should be visible if that file was modified since the latest previous LAYOUTCOMMIT or LAYOUTGET. 3.5.2 LAYOUTCOMMIT and size The file's size may be updated at LAYOUTCOMMIT time as well. The LAYOUTCOMMIT operation contains an argument that indicates the last byte offset to which the client wrote ("lastbytewritten"). Note: for this offset to be viewed as a file size it must be incremented by one byte (a write to offset 0 would map into a file size of 1, but the last byte written is 0). The metadata server may do one of the following: 1. It may update the file's size based on the last byte written offset. However, to the extent possible, the metadata server should sanity check any value to which the file's size is going to be set. E.g., it must not truncate the file based on the client presenting a smaller last byte written offset than the file's current size. 2. If it has sufficient other knowledge of file size (e.g., by querying the storage devices through the management protocol), it may ignore the client provided argument and use the query-derived value. 3. It may use the last byte written offset as a hint, subject to correction when other information is available as above. The method chosen to update the file's size will depend on the storage device's and/or the management protocol's implementation. For example, if the storage devices are block devices with no knowledge of file size, the metadata server must rely on the client to set the size appropriately. A new size flag and length are also returned in the results of a LAYOUTCOMMIT. This union indicates whether a new size was set, and to what length it was set. If a new size is set as a result of LAYOUTCOMMIT, then the metadata server must reply with the new size. As well, if the size is updated, the metadata server in conjunction with the management protocol SHOULD ensure that the new size is reflected by the storage devices immediately upon return of the LAYOUTCOMMIT operation; e.g., a READ up to the new file size should succeed on the storage devices (assuming no intervening truncations). Again, if the client wants to explicitly grow or shrink a file, SETATTR must be used. Welch, et al. Expires January 16, 2006 [Page 18] Internet-Draft pNFS Operations July 2005 Since client layout holders may be unaware of changes made to the file's size (through LAYOUTCOMMIT or SETATTR) by other clients, an additional callback/notification has been added for pNFS. CB_SIZECHANGED is a notification that the metadata server sends to layout holders to notify them of a change in file size. This is preferred over issuing CB_LAYOUTRECALL to each of the layout holders. 3.5.3 LAYOUTCOMMIT and layoutupdate The LAYOUTCOMMIT operation contains a "layoutupdate" argument. This argument is a layout type specific structure. The structure can be used to pass arbitrary layout type specific information from the client to the metadata server at LAYOUTCOMMIT time. For example, if using a block layout, the client can indicate to the metadata server which reserved or allocated blocks it used and which it did not. The "layoutupdate" structure need not be the same structure as the layout returned by LAYOUTGET. The structure is defined by the layout type and is opaque to LAYOUTCOMMIT. 3.6 Crash Recovery Crash recovery is complicated due to the distributed nature of the pNFS protocol. In general, crash recovery for layouts is similar to crash recovery for delegations in the base NFSv4 protocol. However, the client's ability to perform I/O without contacting the metadata server introduces subtleties that must be handled correctly if file system corruption is to be avoided. 3.6.1 Leases The layout lease period plays a critical role in crash recovery. Depending on the capabilities of the storage protocol, it is crucial that the client is able to maintain an accurate layout lease timer to ensure that I/Os are not issued to storage devices after expiration of the layout lease period. In order for the client to do so, it must know which operations renew a lease. 3.6.1.1 Lease Renewal The current NFSv4 specification allows for implicit lease renewals to occur upon receiving an I/O. However, due to the distributed pNFS architecture, implicit lease renewals are limited to operations performed at the metadata server (including I/O performed through the metadata server). So, a client must not assume that READ and WRITE I/O to storage devices implicitly renew lease state. If sessions are required for pNFS, as has been suggested, then the SEQUENCE operation is to be used to explicitly renew leases. It is Welch, et al. Expires January 16, 2006 [Page 19] Internet-Draft pNFS Operations July 2005 proposed that the SEQUENCE operation be extended to return all the specific information that RENEW does, but not as an error as RENEW returns it. Since, when using session, beginning each compound with the SEQUENCE op allows renews to be performed without an additional operation and without an additional request. Again, the client must not rely on any operation to the storage devices to renew a lease. Using the SEQUENCE operation for renewals, simplifies the client's perception of lease renewal. 3.6.1.2 Client Lease Timer Depending on the storage protocol and layout type in use, it may be crucial that the client not issue I/Os to storage devices if the corresponding layout's lease has expired. Doing so may lead to file system corruption if the layout has been given out and used by another client. In order to prevent this, the client must maintain an accurate lease timer for all layouts held. RFC3530 has the following to say regarding the maintenance of a client lease timer: ...the client must track operations which will renew the lease period. Using the time that each such request was sent and the time that the corresponding reply was received, the client should bound the time that the corresponding renewal could have occurred on the server and thus determine if it is possible that a lease period expiration could have occurred. To be conservative, the client should start its lease timer based on the time that the it issued the operation to the metadata server, rather than based on the time of the response. It is also necessary to take propagation delay into account when requesting a renewal of the lease: ...the client should subtract it from lease times (e.g., if the client estimates the one-way propagation delay as 200 msec, then it can assume that the lease is already 200 msec old when it gets it). In addition, it will take another 200 msec to get a response back to the server. So the client must send a lock renewal or write data back to the server 400 msec before the lease would expire. Thus, the client must be aware of the one-way propagation delay and should issue renewals well in advance of lease expiration. Clients, to the extent possible, should try not to issue I/Os that may extend past the lease expiration time period. However, since this is not always possible, the storage protocol must be able to protect against the effects of inflight I/Os, as is discussed later. Welch, et al. Expires January 16, 2006 [Page 20] Internet-Draft pNFS Operations July 2005 3.6.2 Client Recovery Client recovery for layouts works in much the same way as NFSv4 client recovery works for other lock/delegation state. When an NFSv4 client reboots, it will lose all information about the layouts that it previously owned. There are two methods by which the server can reclaim these resources and allow otherwise conflicting layouts to be provided to other clients. The first is through the expiry of the client's lease. If the client recovery time is longer than the lease period, the client's lease will expire and the server will know that state may be released. for layouts the server may release the state immediately upon lease expiry or it may allow the layout to persist awaiting possible lease revival, as long as there are no conflicting requests. On the other hand, the client may recover in less time than it takes for the lease period to expire. In such a case, the client will contact the server through the standard SETCLIENTID protocol. The server will find that the client's id matches the id of the previous client invocation, but that the verifier is different. The server uses this as a signal to release all the state associated with the client's previous invocation. 3.6.3 Metadata Server Recovery The server recovery case is slightly more complex. In general, the recovery process again follows the standard NFSv4 recovery model: the client will discover that the metadata server has rebooted when it receives an unexpected STALE_STATEID or STALE_CLIENTID reply from the server; it will then proceed to try to reclaim its previous delegations during the server's recovery grace period. However, layouts are not reclaimable in the same sense as data delegations; there is no reclaim bit, thus no guarantee of continuity between the previous and new layout. [OPEN ISSUE: there is no reclaim bit for getting a layout. Currently layouts obtained through LAYOUTGET make no guarantee of continuity in the case of reclaiming an old layout. Recall, a layout is not required to perform I/O. I/O can always be performed through the metadata server. If a reclaim bit existed a block layout type might be happier knowing it got the layout back with the assurance of continuity. However, this would require the metadata server trusting the client in telling it the exact layout it had (i.e., the full block-list); maybe too much trust?] If the client has dirty data that it needs to write out, or an outstanding LAYOUTCOMMIT, the client should try to obtain a new Welch, et al. Expires January 16, 2006 [Page 21] Internet-Draft pNFS Operations July 2005 layout covering the byte range covering the previous layout. However, the client might not not get the same layout it had. The range might be different or it might get the same range but the content of the layout might be different. For example, if using a block-based layout, the blocks provisionally assigned by the layout might be different, in which case the client will have to write the corresponding blocks again (and it might decide in the interests of simplicity to always write them again). Alternatively, the client might be unable to obtain a new layout and thus, must write the data using normal NFSv4 through the metadata server. There is an important safety concern associated with layouts that does not come into play in the standard NFSv4 case. If a standard NFSv4 client makes use of a stale delegation, while reading, the consequence could be to deliver stale data to an application. If writing, using a stale delegation or a stale state stateid for an open or lock would result in the rejection of the client's write with the appropriate stale stateid error. However, the pNFS layout enables the client to directly access the file system storage---if this access is not properly managed by the NFSv4 server the client can potentially corrupt the file system data or metadata. Thus, it is vitally important that the client discover that the metadata server has rebooted, and that the client stops using stale layouts before the metadata server gives them away to other clients. To ensure this, the client must be implemented so that layouts are never used to access the storage after the client's lease timer has expired. It is crucial that clients have precise knowledge of the lease periods of their layouts. For specific details on lease renewal and client lease timers, see Section 3.6.1. The prohibition on using stale layouts applies to all layout related accesses, especially the flushing of dirty data to the storage devices. If the client's lease timer expires because the client could not contact the server for any reason, the client MUST immediately stop using the layout until the server can be contacted and the layout can be officially recovered or reclaimed. However, this is only part of the solution. It is also necessary to deal with the consequences of I/Os already in flight. The issue of the effects of I/Os started before lease expiration and possibly continuing through lease expiration is the responsibility of the data storage protocol and as such is layout type specific. There are two approaches the data storage protocol can take. The protocol may adopt a global solution which prevents all I/Os from being executed after the lease expiration (and thus is safe against a client who issues I/Os after lease expiration). This is the preferred solution and the solution used by NFSv4 file based layouts Welch, et al. Expires January 16, 2006 [Page 22] Internet-Draft pNFS Operations July 2005 (see Section 5.6). Alternatively, the storage protocol may rely on proper client operation and only deal with the effects of lingering I/Os. These solutions may impact the client layout-driver, the metadata server layout-driver, and the management protocol. 4. Security Considerations The pNFS extension partitions the NFSv4 file system protocol into two parts, the control path and the data path (storage protocol). The control path contains all the new operations described by this extension; all existing NFSv4 security mechanisms and features apply to the control path. The combination of components in a pNFS system (see Figure 1) is required to preserve the security properties of NFSv4 with respect to an entity accessing data via a client, including security countermeasures to defend against threats that NFSv4 provides defenses for in environments where these threats are considered significant. In some cases, the security countermeasures for connections to storage devices may take the form of physical isolation or a recommendation not to use pNFS in an environment. For example, it is currently infeasible to provide confidentiality protection for some storage device access protocols to protect against eavesdropping; in environments where eavesdropping on such protocols is of sufficient concern to require countermeasures, physical isolation of the communication channel (e.g., via direct connection from client(s) to storage device(s)) and/or a decision to forego use of pNFS (e.g., and fall back to NFSv4) may be appropriate courses of action. In full generality where communication with storage devices is subject to the same threats as client-server communication, the protocols used for that communication need to provide security mechanisms comparable to those available via RPSEC_GSS for NFSv4. Many situations in which pNFS is likely to be used will not be subject to the overall threat profile for which NFSv4 is required to provide countermeasures. pNFS implementations MUST NOT remove NFSv4's access controls. The combination of clients, storage devices, and the server are responsible for ensuring that all client to storage device file data access respects NFSv4 ACLs and file open modes. This entails performing both of these checks on every access in the client, the storage device, or both. If a pNFS configuration performs these checks only in the client, the risk of a misbehaving client obtaining unauthorized access is an important consideration in determining when it is appropriate to use such a pNFS configuration. Such configurations SHOULD NOT be used when client- only access checks do not provide sufficient assurance that NFSv4 access control is being Welch, et al. Expires January 16, 2006 [Page 23] Internet-Draft pNFS Operations July 2005 applied correctly. The following subsections describe security considerations specifically applicable to each of the three major storage device protocol types supported for pNFS. [Additional security info - the object protocol needs this, but it may be out-of-band; the OSD experts will know for sure. For Block and File an approach of the client being expected to know what it needs when it sees what it's being asked to access probably suffices, although we might be able to help (e.g., pass iSCSI CHAP authentication identities, but NOT secrets, via pNFS). For File in particular, defaulting to the NFSv4 principal is probably a good idea, although it's not strictly necessary.] [Requiring strict equivalence to NFSv4 security mechanisms is the wrong approach. Will need to lay down a set of statements that each protocol has to make starting with access check location/properties.] 4.1 File Layout Security A NFSv4 file layout type is defined in Section 5; see Section 5.7 for additional security considerations and details. In summary, the NFSv4 file layout type requires that all I/O access checks MUST be performed by the storage devices, as defined by the NFSv4 specification. If another file layout type is being used, additional access checks may be required. But in all cases, the access control performed by the storage devices must be at least as strict as that specified by the NFSv4 protocol. 4.2 Object Layout Security The object storage protocol relies on a cryptographically secure capability to control accesses at the object storage devices. Capabilities are generated by the metadata server, returned to the client, and used by the client as described below to authenticate their requests to the Object Storage Device (OSD). Capabilities therefore achieve the required access and open mode checking. They allow the file server to define and check a policy (e.g., open mode) and the OSD to check and enforce that policy without knowing the details (e.g., user IDs and ACLs). Since capabilities are tied to layouts, and since they are used to enforce access control, the server should recall layouts and revoke capabilities when the file ACL or mode changes in order to signal the clients. Each capability is specific to a particular object, an operation on that object, a byte range w/in the object, and has an explicit expiration time. The capabilities are signed with a secret key that Welch, et al. Expires January 16, 2006 [Page 24] Internet-Draft pNFS Operations July 2005 is shared by the object storage devices (OSD) and the metadata managers. clients do not have device keys so they are unable to forge capabilities. The details of the security and privacy model for Object Storage are out of scope of this document and will be specified in the Object Storage version of the storage protocol definition. However, the following sketch of the algorithm should help the reader understand the basic model. LAYOUTGET returns {CapKey = MAC(CapArgs), CapArgs} The client uses CapKey to sign all the requests it issues for that object using the respective CapArgs. In other words, the CapArgs appears in the request to the storage device, and that request is signed with the CapKey as follows: ReqMAC = MAC(Req, Nonceln) The following is sent to the OSD: {CapArgs, Req, Nonceln, ReqMAC}. The OSD uses the SecretKey it shares with the metadata server to compare the ReqMAC the client sent with a locally computed MAC(CapArgs)>(Req, Nonceln) and if they match the OSD assumes that the capabilities came from an authentic metadata server and allows access to the object, as allowed by the CapArgs. Therefore, if the server LAYOUTGET reply, holding CapKey and CapArgs, is snooped by another client, it can be used to generate valid OSD requests (within the CapArgs access restriction). To provide the required privacy requirements for the capabilities returned by LAYOUTGET, the GSS-API can be used, e.g. by using a session key known to the file server and to the client to encrypt the whole layout or parts of it. Two general ways to provide privacy in the absence of GSS-API that are independent of NFSv4 are either an isolated network such as a VLAN or a secure channel provided by IPsec. 4.3 Block Layout Security As typically used, block protocols rely on clients to enforce file access checks since the storage devices are generally unaware of the files they are storing (and in particular are unaware of which blocks belongs to which file). In such environments, the physical addresses of blocks are exported to pNFS clients via layouts. An alternative Welch, et al. Expires January 16, 2006 [Page 25] Internet-Draft pNFS Operations July 2005 method of block protocol use is for the storage devices to export virtualized block addresses, which do reflect the files to which blocks belong. These virtual block addresses are exported to pNFS clients via layouts. This allows the storage device to make appropriate access checks, while mapping virtual block addresses to physical block addresses. In environments where access control is important and client-only access checks provide insufficient assurance of access control enforcement (e.g., there is concern about a malicious of malfunctioning client skipping the access checks) and where physical block addresses are exported to clients, the storage devices will generally be unable to compensate for these client deficiencies. In such threat environments, block protocols SHOULD NOT be used with pNFS, unless the data server is able to implement the appropriate access checks, via use of virtualized block addresses, or other means. NFSv4 without pNFS or pNFS with a different type of storage protocol would be a more suitable means to access files in such environments. Storage-device/protocol-specific methods (e.g. LUN masking/mapping) may be available to prevent malicious or high-risk clients from directly accessing storage devices. 5. NFSv4 File Layout Type This section describes the semantics and format of NFSv4 file-based layouts. 5.1 File Striping and Data Access The file layout type describes a method for striping data across multiple devices. The data for each stripe unit is stored within an NFSv4 file located on a particular storage device. The structures used to describe the stripe layout are as follows: Welch, et al. Expires January 16, 2006 [Page 26] Internet-Draft pNFS Operations July 2005 enum stripetype4 { STRIPE_SPARSE = 1, STRIPE_DENSE = 2 }; struct nfsv4_file_layout { /* Per device info */ pnfs_deviceid4 dev_id; nfs_fh4 fh; }; struct nfsv4_file_layouttype4 { stripetype4 stripe_type; uint64_t stripe_unit; length4 file_size; nfsv4_file_layout dev_list<>; }; The file layout specifies an ordered array of (deviceID, filehandle) tuples, as well as the stripe size, type of stripe layout (discussed a little later), and the file's current size (current as of LAYOUTGET time). The filehandle, "fh", identifies the file on a storage device identified by "dev_id", that holds a particular stripe of the file. The stripe width is determined by the stripe unit size multiplied by the number of devices in the dev_list. The stripe held by (dev_id, fh) is determined by that tuples position within the device list, "dev_list". For example, consider a dev_list consisting of the following (dev_id, fh) pairs: <(1,0x12), (2,0x13), (1,0x15)> and stripe_unit = 32KB The stripe width is 32KB * 3 devices = 96KB. The first entry specifies that on device 1 in the data file with filehandle 0x12 holds the first 32KB of data (and every 32KB stripe beginning where the file's offset % 96KB == 0). Notice, devices and filehandles may be repeated multiple times within the device list array (as is shown where storage device 1 holds both the first and third stripe of data). Data is striped across the devices in the order listed in the device list array in increments of the stripe size. A data file stored on a storage device MUST map to a single file as defined by the metadata server; i.e., data from two files as viewed by the metadata server MUST NOT be stored within the same data file on any storage device. The "stripe_type" field specifies how the data is laid out within the data file on a storage device. It allows for two different data layouts: sparse and dense or packed. The stripe type determines the calculation that must be made to map the file's offset (as visible to Welch, et al. Expires January 16, 2006 [Page 27] Internet-Draft pNFS Operations July 2005 the client) to the offset within the data file located on the storage device. 5.1.1 Sparse and Dense Storage Device Data Layouts The stripe_type field allows for two storage device data file representations. Example sparse and dense storage device data layouts are illustrated below: Sparse file-layout (stripe_unit = 4KB) ------------------ Is represented by the following file layout on the storage devices: Offset ID:0 ID:1 ID:2 0 +--+ +--+ +--+ +--+ indicates a |//| | | | | |//| stripe that 4KB +--+ +--+ +--+ +--+ contains data | | |//| | | 8KB +--+ +--+ +--+ | | | | |//| 12KB +--+ +--+ +--+ |//| | | | | 16KB +--+ +--+ +--+ | | |//| | | +--+ +--+ +--+ The sparse file-layout has holes for the byte ranges not exported by that storage device. This allows clients to access data using the real offset into the file, regardless of the storage device's position within the stripe. However, if a client writes to one of the holes (e.g., offset 4-12KB on device 1), then an error MUST be returned by the storage device. This requires that the storage device have knowledge of the layout for each file. When using a sparse layout, the offset into the storage device data file is the same as the offset into the main file. Welch, et al. Expires January 16, 2006 [Page 28] Internet-Draft pNFS Operations July 2005 Dense/packed file-layout (stripe_unit = 4KB) ------------------------ Is represented by the following file layout on the storage devices: Offset ID:0 ID:1 ID:2 0 +--+ +--+ +--+ |//| |//| |//| 4KB +--+ +--+ +--+ |//| |//| |//| 8KB +--+ +--+ +--+ |//| |//| |//| 12KB +--+ +--+ +--+ |//| |//| |//| 16KB +--+ +--+ +--+ |//| |//| |//| +--+ +--+ +--+ The dense or packed file-layout does not leave holes on the storage devices. Each stripe unit is spread across the storage devices. As such, the storage devices need not know the file's layout since the client is allowed to write to any offset. The calculation to determine the byte offset within the data file for dense storage device layouts is: stripe_width = stripe_unit * N; where N = |dev_list| dev_offset = floor(file_offset / stripe_width) * stripe_unit + file_offset % stripe_unit Regardless of the storage device data file layout, the calculation to determine the index into the device array is the same: dev_idx = floor(file_offset / stripe_unit) mod N 5.1.2 Operations Issued to Storage Devices Clients MUST use the filehandle described within the layout when accessing data on the storage devices. When using the layout's filehandle, the client MUST only issue READ, WRITE, PUTFH, COMMIT, and NULL operations to the storage device associated with that filehandle. If a client issues an operation other than those specified above, using the filehandle and storage device listed in the client's layout, that storage device SHOULD return an error to the client. The client MUST follow the instruction implied by the layout (which filehandles to use on which devices). As described in Section 3.2, a client MUST NOT issue I/Os to storage devices for Welch, et al. Expires January 16, 2006 [Page 29] Internet-Draft pNFS Operations July 2005 which it does not hold a valid layout. The storage devices may reject such requests. [OPEN ISSUE: Should SHOULD be should] GETATTR and SETATTR MUST be directed to the metadata server. In the case of a SETATTR of the size attribute, the management protocol is responsible for propagating size updates/truncations to the storage devices. In the case of extending WRITEs to the storage devices, the new size must be visible on the metadata server once a LAYOUTCOMMIT has completed (see Section 3.5.2, Section 5.5.2). All size attribute updates MUST be effective on the storage devices immediately (by the time the metadata operation returns), so that READs past EOF can be recognized. 5.2 Global Stateid Requirements Note, there are no stateids returned embedded within the layout. The client MUST use the stateid representing open or lock state as returned by an earlier metadata operation (e.g., OPEN, LOCK), or a special stateid to perform I/O on the data-servers (as in regular NFSv4). Special stateid usage for I/O is subject to the NFSv4 protocol specification. The stateid used for I/O MUST have the same effect and be subject to the same validation on storage device as it would if the I/O was being performed on the metadata server itself (in the absence of pNFS). This has the implication that stateids are globally valid on both the metadata and storage devices. This requires the metadata server to propagate changes in lock and open state to the data-servers, so that the data-servers can validate I/O accesses. This is discussed further in Section 5.4. 5.3 The Layout Iomode The layout iomode need not used by the metadata server when servicing NFSv4 file-based layouts, although in some circumstances it may be useful to use. For example, if the server implementation supports reading from read-only replicas or mirrors, it would be useful for the server to return a layout enabling the client to do so. As such, the client should set the iomode based on its intent to read or write the data. The client may default to an iomode of READ/WRITE. The iomode need not be checked by the storage devices when clients perform I/O. However, the storage devices SHOULD still validate that the client holds a valid layout and return an error if the client does not. [OPEN ISSUE: Again, requiring storage devices to validate that clients hold valid layouts, requires propagating layouts to storage devices. This is not possible if using vanilla NFSv4 storage Welch, et al. Expires January 16, 2006 [Page 30] Internet-Draft pNFS Operations July 2005 devices.] 5.4 Storage Device State Propagation Since the metadata server, which handles lock and open-mode state changes, as well as ACLs, may not be collocated with the storage devices (where I/O access is validated), the server implementation MUST take care of propagating changes of this state to the storage devices. Once the propagation to the storage devices is complete, the full effect of those changes must be in effect at the storage devices. However, some state changes need not be propagated immediately, although all changes SHOULD be propagated promptly. These state propagations have an impact on the design of the management protocol, even though the management protocol is outside of the scope of this specification. Immediate propagation refers to the synchronous propagation of state from the metadata server to the storage device(s); the propagation must be complete before returning to the client. 5.4.1 Lock State Propagation Mandatory locks MUST be made effective at the storage devices before the request that establishes them returns to the caller. Thus, mandatory lock state MUST be synchronously propagated to the storage devices. On the other hand, since advisory lock state is not used for checking I/O accesses at the storage devices, there is no semantic reason for propagating advisory lock state to the storage devices. However, since all lock, unlock, open downgrades and upgrades affect the sequence ID stored within the stateid, the stateid changes which may cause difficulty if this state is not propagated. Thus, when a client uses a stateid on a storage device for I/O with a newer sequence number than the one the storage device has, the storage device should query the metadata server and get any pending updates to that stateid. This allows stateid sequence number changes to be propagated lazily, on-demand. [OPEN ISSUE: How does the requirement of sessions affect the propagation of stateid sequence numbers?] Since updates to advisory locks neither confer nor remove privileges, these changes need not be propagated immediately, and may not need to be propagated promptly. The updates to advisory locks need only be propagated when the storage device needs to resolve a question about a stateid. In fact, if byte-range locking is not mandatory (is advisory) the clients are advised not to use the lock-based stateids for I/O at all. The stateids returned by open are sufficient and eliminate overhead for this kind of state propagation. Welch, et al. Expires January 16, 2006 [Page 31] Internet-Draft pNFS Operations July 2005 5.4.2 Open-mode Validation Open-mode validation MUST be performed against the open mode(s) held by the storage devices. However, the server implementation may not always require the immediate propagation of changes. Reduction in access because of CLOSEs or DOWNGRADEs do not have to be propagated immediately, but SHOULD be propagated promptly (whereas changes due to revocation MUST be propagated immediately). On the other hand, changes that expand access (e.g., new OPEN's and upgrades) don't have to be propagated immediately but the storage device SHOULD NOT reject a request because of mode issues without making sure that the upgrade is not in flight. 5.4.3 File Attributes Since the SETATTR operation has the ability to modify state that is visible on both the metadata and storage devices (e.g., the size), care must be taken to ensure that the resultant state (across the set of storage devices) is consistent; especially when truncating or growing the file. As described earlier, the LAYOUTCOMMIT operation is used to ensure that the metadata is synced with changes made to the storage devices. For the file-based protocol, it is necessary to re-sync state such as the size attribute, and the setting of mtime/atime. See Section 3.5 for a full description of the semantics regarding LAYOUTCOMMIT and attribute synchronization. It should be noted, that by using a file- based layout type, it is possible to synchronize this state before LAYOUTCOMMIT occurs. For example, the management protocol can be used to query the attributes present on the storage devices. Any changes to file attributes that control authorization (or access) as reflected by ACCESS calls or READs and WRITEs on the metadata server, MUST be propagated to the storage devices for enforcement on READ and WRITE I/O calls. If the changes made on the metadata server result in more restrictive access permissions for any user, those changes MUST be propagated to the storage devices synchronously. Recall that the NFSv4 protocol [2] specifies that: ...since the NFS version 4 protocol does not impose any requirement that READs and WRITEs issued for an open file have the same credentials as the OPEN itself, the server still must do appropriate access checking on the READs and WRITEs themselves. This also includes changes to ACLs. The propagation of access right changes due to changes in ACLs may be asynchronous only if the server implementation is able to determine that the updated ACL is not more Welch, et al. Expires January 16, 2006 [Page 32] Internet-Draft pNFS Operations July 2005 restrictive for any user specified in the old ACL. Due to the relative infrequency of ACL updates, it is suggested that all changes be propagated synchronously. [OPEN ISSUE: it has been suggested that the NFSv4 specification is in error with regard to allowing principles other than those used for OPEN to be used for file I/O. It has been suggested that it should be fixed here by pNFS]. 5.5 Extending file size 5.5.1 READs and EOF A potential problem exists when a data file on a particular storage device is grown past EOF; it exists for both dense and sparse layouts. Imagine the following scenario: a client creates a new file (size == 0) and writes to byte 128KB; the client then seeks to the beginning of the file and reads byte 100. The client should receive 0s back as a result of the read. However, if the read falls on a different storage device to the client's original write, the storage device servicing the READ may still believe that the file's size is at 0 and return no data (with the EOF flag set). The storage device can only return 0s if it knows that the file's size has been extended. This would require the immediate propagation of the file's size to all storage devices, which is potentially very costly, instead, another approach as outlined below. First, the file's size is returned within the layout by LAYOUTGET. This size must reflect the latest size at the metadata server as set by the most recent of either the last LAYOUTCOMMIT or SETATTR; however, it may be more recent. Second, if a client performs a read that is returned short (i.e., is fully within the file's size, but the storage device indicates EOF and returns partial or no data), the client must assume that it is a hole and substitute 0s for the data not read (up until its known local file size). If a client extends the file, it must update its local file size. Third, if the metadata server receives a SETATTR of the size or a LAYOUTCOMMIT that alters the file's size, the metadata server MUST send out CB_SIZECHANGED messages with the new size to clients holding layouts (it need not send a notification to the client that performed the operation that resulted in the size changing). Upon reception of the CB_SIZECHANGED notification, clients must update their local size for that file. As well, if a new file size is returned as a result to LAYOUTCOMMIT, the client must update their local file size. 5.5.2 LAYOUTCOMMIT and EOF Another complication can arise due to EOF. If a file has been grown Welch, et al. Expires January 16, 2006 [Page 33] Internet-Draft pNFS Operations July 2005 by a set of WRITEs prior to a LAYOUTCOMMIT, the management protocol must ensure that the corresponding file on each storage device is grown (possibly sparsely) up until the offset represented by the EOF length before LAYOUTCOMMIT returns. For example: Imagine a file is striped across four storage devices, using a sparse file layout, with 64KB on each storage device. A WRITE of 64KB occurs starting at offset 192KB (the first stripe on the 4th storage device) followed by a LAYOUTCOMMIT. The new EOF offset is now at 256KB, however the corresponding file size on the first three storage devices is 0, since they did not service any WRITE operations. Immediately upon completion of LAYOUTCOMMIT, the server implementation MUST ensure that READs to any of the storage devices, at an offset below EOF, succeed; indeed, in this example, a read to any of the first three storage devices (below EOF) must return all 0s. The easiest way to accomplish this is to set the file size on each of the storage devices to EOF. Note, this only need occur at LAYOUTCOMMIT time or upon the reception of a SETATTR that modifies the size. 5.6 Crash Recovery Considerations As described in Section 3.6, the layout type specific storage protocol is responsible for handling the effects of I/Os started before lease expiration, extending through lease expiration. The NFSv4 file layout type prevents all I/Os from being executed after lease expiration, without relying on a precise client lease timer and without requiring storage devices to maintain lease timers. It works as follows. In the presence of sessions, each compound begins with a SEQUENCE operation that contains the "clientID". On the storage device, the clientID can be used to validate that the client has a valid layout for the I/O being performed, if it does not, the I/O is rejected. Before the metadata server takes any action to invalidate a layout given out by a previous instance, it must make sure that all layouts from that previous instance are invalidated at the storage devices. Note: it is sufficient to invalidate the stateids associated with the layout only if special stateids are not being used for I/O at the storage devices, otherwise the layout itself must be invalidated. This means that a metadata server may not restripe a file until it has contacted all of the storage devices to invalidate the layouts from the previous instance nor may it give out locks that conflict with locks embodied by the stateids associated with any layout from the previous instance without either doing a specific invalidation (as it would have to do anyway) or doing a global storage device invalidation. Welch, et al. Expires January 16, 2006 [Page 34] Internet-Draft pNFS Operations July 2005 5.7 Security Considerations The NFSv4 file layout type MUST adhere to the security considerations outlined in Section 4. More specifically, storage devices must make all of the required access checks on each READ or WRITE I/O as determined by the NFSv4 protocol [2]. This impacts the management protocol and the propagation of state from the metadata server to the storage devices; see Section 5.4 for more details. 5.8 Alternate Approaches Two alternate approaches exist for file-based layouts and the method used by clients to obtain stateids used for I/O. Both approaches embed stateids within the layout. However, before examining these approaches it is important to understand the distinction between clients and owners. Delegations belong to clients, while locks (record and share reservations) are held by owners (who in turn belong to a specific client). As such, delegations can only protect against inter-client conflicts, not intra-client conflicts. Layouts are held by clients and SHOULD NOT be associated with state held by owners. Therefore, if stateids used for data access are embedded within a layout, these stateids can only act as delegation stateids, protecting against inter-client conflicts; stateids pertaining to an owner can not be embedded within the layout. This has the implication that the client MUST arbitrate among all intra-client conflicts (such as arbitrating among lock requests by different processes) before issuing pNFS operations. Using the stateids stored within the layout, storage devices can only arbitrate between clients (not owners). The first alternate approach is to do away with global stateids (stateids returned by OPEN/LOCK that are valid on the metadata server and storage devices) and use only stateids embedded within the layout. This approach has the drawback that the stateids used for I/O access can not be validated against per owner state (rather they are validated against per client state), since they are only associated with the client holding the layout. It breaks the semantics of tieing a stateid used for I/O to an open instance. This has the implication that clients must delegate per owner lock and open requests internally, rather than push the work onto the storage devices. The storage devices can still arbitrate and enforce inter- client lock and open state. The second approach is a hybrid approach. This approach allows for stateids to be embedded with the layout, but also allows for the possibility of global stateids. If the stateid embedded within the layout is a special stateid of all zeros, then the stateid referring Welch, et al. Expires January 16, 2006 [Page 35] Internet-Draft pNFS Operations July 2005 to the last successful OPEN/LOCK should be used (as a global stateid presented earlier in the proposal). This approach is recommended if it is decided that using NFSv4 as a management protocol is required. This proposal suggests the global stateid approach due to the cleaner semantics it provides regarding the relationship between stateids used for I/O and their corresponding open instance (or lock state). However, it does have a profound impact on the management protocol's implementation and the state propagation that is required (as described in Section 5.4). 6. pNFS Typed Data Structures 6.1 pnfs_layouttype4 enum pnfs_layouttype4 { LAYOUT_NFSV4_FILES = 1 }; A layout type specifies the layout being used. The implication is that clients have "layout drivers" that support one or more layout types. The file server advertises the layout types it supports through the LAYOUT_TYPES file system attribute. A client asks for layouts of a particular type in LAYOUTGET, and passes those layouts to its layout driver. The set of well known layout types must be defined. As well, a private range of layout types should exist and also be well defined. This would allow custom installations to introduce new layout types. [OPEN ISSUE: It must be decided whether IANA should control the namespace of layout types, or whether each new layout type must go through the specification process (probably as a minor version extension)] The LAYOUT_NFSV4_FILES enumeration specifies that the NFSv4 file layout type is to be used. 6.2 pnfs_deviceid4 typedef uint32_t pnfs_deviceid4; /* 32-bit device ID */ Layout information includes device IDs that specify a storage device through a compact handle. Addressing and type information is obtained with the GETDEVICEINFO operation. A client must not assume that device IDs are valid across metadata server reboots. The device ID is qualified by the layout type. This allows different layout drivers to generate device IDs without the need for co-ordination. See Section 3.1.1 for more details. Welch, et al. Expires January 16, 2006 [Page 36] Internet-Draft pNFS Operations July 2005 6.3 pnfs_devaddr4 union pnfs_devaddr4 switch (pnfs_layouttype4 layout_type) { case LAYOUT_NFSV4_FILES: string r_netid<>; /* network ID */ string r_addr<>; /* universal address */ default: opaque devaddr<>; /* For other layouts */ }; The device address is used to set up a communication channel with the storage device. Different layout types will require different types of structures to define how they communicate with storage devices. The union is switched on the layout type. Currently, the only device address defined is that for the NFSv4 file layout, which identifies a storage device by network IP address and port number. This is sufficient for the clients to communicate with the NFSv4 storage devices, and may also be sufficient for object-based storage drivers to communicate with OSDs. 6.4 pnfs_devlist_item4 struct pnfs_devlist_item4 { pnfs_deviceid4 id; pnfs_deviceaddr4 addr; }; An array of these values is returned by the GETDEVICELIST operation. They define the set of devices associated with a file system. 6.5 pnfs_layout4 union pnfs_layouttypes4 switch (pnfs_layouttype4 layout_type) { case LAYOUT_NFSV4_FILES: pnfs_nfsv4_layouttype4 file_layout; default: opaque layout_data<>; }; struct pnfs_layout4 { offset4 offset; length4 length; pnfs_layoutiomode4 iomode; pnfs_layouttypes4 layout; }; The pnfs_layout4 structure defines a layout for a file. The pnfs_layouttypes4 union contains the portion of the layout specific Welch, et al. Expires January 16, 2006 [Page 37] Internet-Draft pNFS Operations July 2005 to the layout type. Currently, only the NFSv4 file layout type is defined; see Section 5.1 for its definition. Since layouts are sub- dividable, the offset and length (together with the file's filehandle, the clientid, iomode, and layout type), identifies the layout. [OPEN ISSUE: it has been suggested that the layout type include a generic striping layer, as defined in Section 5.1. This has not yet been done.] 6.6 pnfs_layoutupdate4 union pnfs_layoutupdate4 switch (pnfs_layouttype4 layout_type) { case LAYOUT_NFSV4_FILES: void; default: opaque layout_data<>; }; The pnfs_layoutupdate4 structure is used by the client to return 'updated' layout information to the metadata server at LAYOUTCOMMIT time. This provides a channel to pass layout type specific information back to the metadata server. E.g., for block layout types this could include the list of reserved blocks that were written. The contents of the structure are determined by the layout type and are defined in their context. 6.7 pnfs_layoutiomode4 enum pnfs_layoutiomode4 { LAYOUTIOMODE_READ = 1, LAYOUTIOMODE_RW = 2, LAYOUTIOMODE_ANY = 3, }; The iomode specifies whether the client intends to read or write (with the possibility of reading) the data represented by the layout. The ANY iomode MUST NOT be used for LAYOUTGET, however, it can be used for LAYOUTRETURN and LAYOUTRECALL. The ANY iomode specifies that layouts pertaining to both READ and RW are being returned or recalled, respectively. The metadata server's use of the iomode may depend on the layout type being used. The storage devices may validate I/O accesses against the iomode (and reject invalid accesses). 7. pNFS File Attributes Welch, et al. Expires January 16, 2006 [Page 38] Internet-Draft pNFS Operations July 2005 7.1 pnfs_layouttype4<> FS_LAYOUT_TYPES This attribute applies to a file system and indicates what layout types are supported by the file system. We expect this attribute to be queried when a client encounters a new fsid. This attribute is used by the client to determine if it has applicable layout drivers. 7.2 pnfs_layouttype4<> FILE_LAYOUT_TYPE This attribute indicates the particular layout type(s) used for a file. This is for informational purposes only. The client needs to use the LAYOUTGET operation in order to get enough information (e.g., specific device information) in order to perform I/O. 7.3 pnfs_layouttypes4 FILE_LAYOUT_HINT This attribute may be set on newly created files to influence the metadata server's choice for the file's layout. It is suggested that this attribute is set as one of the initial attributes within the OPEN call. The metadata server may ignore this attribute. This attribute is a sub-set of the layout returned by LAYOUTGET. For example, instead of specifying particular devices, this would be used to suggest the stripe width of a file. It is up to the server implementation to determine which fields within the layout it uses. 7.4 uint32_t FS_LAYOUT_PREFERRED_BLOCKSIZE This attribute is a file system wide attribute and indicates the preferred block size for direct storage device access. 7.5 uint32_t FS_LAYOUT_PREFERRED_ALIGNMENT This attribute is a file system wide attribute and indicates the preferred alignment for direct storage device access. 8. pNFS Error Definitions NFS4ERR_BADLAYOUT Layout specified is invalid. NFS4ERR_BADIOMODE Layout iomode is invalid. NFS4ERR_LAYOUTUNAVAILABLE Layouts are not available for the file or its containing file system. NFS4ERR_LAYOUTTRYLATER Layouts are temporarily unavailable for the file, client should retry later. Welch, et al. Expires January 16, 2006 [Page 39] Internet-Draft pNFS Operations July 2005 NFS4ERR_UNKNOWN_LAYOUTTYPE Layout type is unknown. 9. pNFS Operations 9.1 LAYOUTGET - Get Layout Information SYNOPSIS (cfh), clientid, layout_type, iomode, offset, length, maxcount -> layout ARGUMENT struct LAYOUTGET4args { /* CURRENT_FH: file */ clientid4 clientid; pnfs_layouttype4 layout_type; pnfs_layoutiomode4 iomode; offset4 offset; length4 length; count4 maxcount; }; RESULT struct LAYOUTGET4resok { pnfs_layout4 layout; }; union LAYOUTGET4res switch (nfsstat4 status) { case NFS4_OK: LAYOUTGET4resok resok4; default: void; }; DESCRIPTION Requests a layout for reading or writing the file given by the filehandle at the byte range specified by offset and length. Layouts are identified through the clientid, filehandle, byte range (offset, length pair), and iomode. The use of the iomode depends upon the layout type, but should reflect the client's data access intent. The LAYOUTGET operation returns layout information for the specified byte range. To get a layout from a specific offset through the end- Welch, et al. Expires January 16, 2006 [Page 40] Internet-Draft pNFS Operations July 2005 of-file (no matter how long the file actually is) use a length field with all bits set to 1 (one). If the length is zero, or if a length which is not all bits set to one is specified, and length when added to the offset exceeds the maximum 64-bit unsigned integer value, the error NFS4ERR_INVAL will result. The "maxcount" field specifies the maximum layout size (in bytes) that the client can handle. If the layout exceeds the size specified by maxcount, the metadata server will return the NFS4ERR_TOOSMALL error. As well, the metadata server may adjust the range of the returned layout based on striping patterns and usage implied by the iomode. The client must be prepared to get a layout that does not line up exactly with their request; there MUST be at least one byte of overlap between the layout returned by the server and the client's request, or the server SHOULD reject the request. See Section 3.3 for more details. The metadata server may also return a layout with an iomode other than that requested by the client. If it does so, it must ensure that the iomode is more permissive than the iomode requested. E.g., this allows an implementation to upgrade read-only requests to read/ write requests at its discretion (within the limits of the layout type specific protocol). An iomode of either LAYOUTIOMODE_READ or LAYOUTIOMODE_RW must be returned. The format of the returned layout is specific to the underlying file system. Layout types other than the NFSv4 file layout type should be specified outside of this document. If layouts are not supported for the requested file or its containing file system the server SHOULD return NFS4ERR_LAYOUTUNAVAILABLE. If the layout type is not supported, the metadata server should return NFS4ERR_UNKNOWN_LAYOUTTYPE. If layouts are supported but no layout matches the client provided layout identification, the server should return NFS4ERR_BADLAYOUT. If an invalid iomode is specified, or an iomode of LAYOUTIOMODE_ANY is specified, the server should return NFS4ERR_BADIOMODE. If the layout for the file is unavailable due to transient conditions, e.g. file sharing prohibits layouts, the server should return NFS4ERR_LAYOUTTRYLATER. If the layout conflicts with a mandatory byte range lock held on the file, and if the storage devices have no method of enforcing mandatory locks, other than through the restriction of layouts, the metadata server should return NFS4ERR_LOCKED. On success, the current filehandle retains its value. Welch, et al. Expires January 16, 2006 [Page 41] Internet-Draft pNFS Operations July 2005 IMPLEMENTATION Typically, LAYOUTGET will be called as part of a compound RPC after an OPEN operation and results in the client having location information for the file; a client may also hold a layout across multiple OPENs. The client specifies a layout type that limits what kind of layout the server will return. This prevents servers from issuing layouts that are unusable by the client. [Comment: The notion of the layout class indicating a sub-set of possible layout types is gone. Now that the class is a flat number space, there is no official way to reference a "class" of layouts (e.g., files, blocks, or objects). This means that the type in the LAYOUTGET may be too restrictive, or that it is up to the server to decide if it can give out a "closely associated" layout that the client may be able to use.] ERRORS NFS4ERR_BADLAYOUT NFS4ERR_BADIOMODE NFS4ERR_FHEXPIRED NFS4ERR_INVAL NFS4ERR_LAYOUTUNAVAILABLE NFS4ERR_LAYOUTTRYLATER NFS4ERR_LOCKED NFS4ERR_NOFILEHANDLE NFS4ERR_NOTSUPP NFS4ERR_STALE NFS4ERR_STALE_CLIENTID NFS4ERR_TOOSMALL NFS4ERR_UNKNOWN_LAYOUTTYPE 9.2 LAYOUTCOMMIT - Commit writes made using a layout Welch, et al. Expires January 16, 2006 [Page 42] Internet-Draft pNFS Operations July 2005 SYNOPSIS (cfh), clientid, offset, length, lastbytewritten, time_modify, time_access, layoutupdate -> newsize ARGUMENT union newtime4 switch (bool timechanged) { case TRUE: nfstime4 time; case FALSE: void; }; union newsize4 switch (bool sizechanged) { case TRUE: length4 size; case FALSE: void; }; struct LAYOUTCOMMIT4args { /* CURRENT_FH: file */ clientid4 clientid; offset4 offset; length4 length; length4 lastbytewritten; newtime4 time_modify; newtime4 time_access; pnfs_layoutupdate4 layoutupdate; }; RESULT struct LAYOUTCOMMIT4resok { newsize4 newsize; }; union LAYOUTCOMMIT4res switch (nfsstat4 status) { case NFS4_OK: LAYOUTCOMMIT4resok resok4; default: void; }; DESCRIPTION Welch, et al. Expires January 16, 2006 [Page 43] Internet-Draft pNFS Operations July 2005 Commits changes in the layout portion represented by the current filehandle, clientid, and byte range. Since layouts are sub- dividable, a smaller portion of a layout, retrieved via LAYOUTGET, may be committed. The region being committed is specified through the byte range (length and offset). Note: the "layoutupdate" structure does not include the length and offset, as they are already specified in the arguments. The LAYOUTCOMMIT operation indicates that the client has completed writes using a layout obtained by a previous LAYOUTGET. The client may have only written a subset of the data range it previously requested. LAYOUTCOMMIT allows it to commit or discard provisionally allocated space and to update the server with a new end of file. The layout referenced by LAYOUTCOMMIT is still valid after the operation completes and can be continued to be referenced by the clientid, filehandle, byte range, and layout type. The "lastbytewritten" field specifies the offset of the last byte written by the client previous to the LAYOUTCOMMIT. Note: this value is never equal to the file's size (at most it is 1 byte less than the file's size). The metadata server may use this information to determine whether the file's size needs to be updated. If the metadata server updates the file's size as the result of the LAYOUTCOMMIT operation, it must return the new size as part of the results. The "time_modify" and "time_access" fields allow the client to suggest times it would like the metadata server to set. The metadata server may use these time values or it may use the time of the LAYOUTCOMMIT operation to set these time values. If the metadata server uses the client provided times, it should sanity check the values (e.g., to ensure time does not flow backwards). If the client wants to force the metadata server to set an exact time, the client should use a SETATTR operation in a compound right after LAYOUTCOMMIT. See Section 3.5 for more details. The "layoutupdate" argument to LAYOUTCOMMIT provides a mechanism for a client to provide layout specific updates to the metadata server. For example, the layout update can describe what regions of the original layout have been used and what regions can be deallocated. There is no NFSv4 file layout specific layoutupdate structure. The layout information is more verbose for block devices than for objects and files because the latter hide the details of block allocation behind their storage protocols. At the minimum, the client needs to communicate changes to the end of file location back to the server, and its view of the file modify and access times (unless it wants the server to set those times to the time of Welch, et al. Expires January 16, 2006 [Page 44] Internet-Draft pNFS Operations July 2005 LAYOUTCOMMIT). For blocks, it needs to specify precisely which blocks have been used. If the layout identified in the arguments does not exist, the error NFS4ERR_BADLAYOUT is returned. The layout being committed may also be rejected if it does not correspond to an existing layout with an iomode of RW. On success, the current filehandle retains its value. [OPEN ISSUE: is it good enough to allow the metadata server to update the change attribute, or should the client be able to direct the metadata server to update it.] ERRORS NFS4ERR_BADLAYOUT NFS4ERR_BADIOMODE NFS4ERR_FHEXPIRED NFS4ERR_INVAL NFS4ERR_NOFILEHANDLE NFS4ERR_STALE NFS4ERR_STALE_CLIENTID NFS4ERR_UNKNOWN_LAYOUTTYPE Welch, et al. Expires January 16, 2006 [Page 45] Internet-Draft pNFS Operations July 2005 9.3 LAYOUTRETURN - Release Layout Information SYNOPSIS (cfh), clientid, offset, length, iomode, layout_type -> - ARGUMENT struct LAYOUTRETURN4args { /* CURRENT_FH: file */ clientid4 clientid; offset4 offset; length4 length; pnfs_layoutiomode4 iomode; pnfs_layouttype4 layout_type; }; RESULT struct LAYOUTRETURN4res { nfsstat4 status; }; DESCRIPTION Returns the layout represented by the current filehandle, clientid, byte range, iomode, and layout type. After this call, the client MUST NOT use the layout and the associated storage protocol to access the file data. The layout being returned may be a subdivision of a layout previously fetched through LAYOUTGET. If the length is all 1s, the layout covers the range from offset to EOF. An iomode of ANY specifies that all layouts that match the other arguments to LAYOUTRETURN (i.e., clientid, byte range, and type) are being returned. Layouts may be returned when recalled or voluntarily (i.e., before the server has recalled them). In either case the client must properly propagate state changed under the context of the layout to storage or to the server before returning the layout. If a client fails to return a layout in a timely manner, then the metadata server should use its management protocol with the storage devices to fence the client from accessing the data referenced by the layout. See Section 3.4 for more details. If the layout identified in the arguments does not exist, the error NFS4ERR_BADLAYOUT is returned. If a layout exists, but the iomode does not match, NFS4ERR_BADIOMODE is returned. Welch, et al. Expires January 16, 2006 [Page 46] Internet-Draft pNFS Operations July 2005 On success, the current filehandle retains its value. [OPEN ISSUE: Should LAYOUTRETURN be modified to handle FSID callbacks?] ERRORS NFS4ERR_BADLAYOUT NFS4ERR_BADIOMODE NFS4ERR_FHEXPIRED NFS4ERR_INVAL NFS4ERR_NOFILEHANDLE NFS4ERR_STALE NFS4ERR_STALE_CLIENTID NFS4ERR_UNKNOWN_LAYOUTTYPE 9.4 GETDEVICEINFO - Get Device Information SYNOPSIS (cfh), device_id, layout_type, maxcount -> device_addr ARGUMENT struct GETDEVICEINFO4args { /* CURRENT_FH: file */ pnfs_deviceid4 device_id; pnfs_layouttype4 layout_type; count4 maxcount; }; RESULT struct GETDEVICEINFO4resok { pnfs_devaddr4 device_addr; }; union GETDEVICEINFO4res switch (nfsstat4 status) { case NFS4_OK: GETDEVICEINFO4resok resok4; default: void; }; DESCRIPTION Returns device type and device address information for a specified Welch, et al. Expires January 16, 2006 [Page 47] Internet-Draft pNFS Operations July 2005 device. The returned device_addr includes a type that indicates how to interpret the addressing information for that device. The current filehandle (cfh) is used to identify the file system; device IDs are unique per file system (FSID) and are qualified by the layout type. At this time we expect two main kinds of device addresses, either IP address and port numbers, or SCSI volume identifiers. The final protocol specification will detail the allowed values for device_type and the format of their associated location information. See Section 3.1.1 for more details on device ID assignment. If the size of the device address exceeds maxcount bytes, the metadata server will return the error NFS4ERR_TOOSMALL. If an invalid device ID is given, the metadata server will respond with NFS4ERR_INVAL. ERRORS NFS4ERR_FHEXPIRED NFS4ERR_INVAL NFS4ERR_TOOSMALL NFS4ERR_UNKNOWN_LAYOUTTYPE Welch, et al. Expires January 16, 2006 [Page 48] Internet-Draft pNFS Operations July 2005 9.5 GETDEVICELIST - Get List of Devices SYNOPSIS (cfh), layout_type, maxcount, cookie, cookie_verf -> device_addrs<> ARGUMENT struct GETDEVICELIST4args { /* CURRENT_FH: file */ pnfs_layouttype4 layout_type; count4 maxcount; nfs_cookie4 cookie; verifier4 cookieverf; }; RESULT struct GETDEVICELIST4resok { pnfs_devlist_item4 device_addrs<>; }; union GETDEVICEINFO4res switch (nfsstat4 status) { case NFS4_OK: GETDEVICEINFO4resok resok4; default: void; }; DESCRIPTION In some applications, especially SAN environments, it is convenient to find out about all the devices associated with a file system. This lets a client determine if it has access to these devices, e.g., at mount time. This operation returns a list of items that establish the association between the short pnfs_deviceid4 and the addressing information for that device, for a particular layout type. This operation may not be able to fetch all device information at once, thus it uses a cookie based approach, similar to READDIR, to fetch additional device information. As in GETDEVICEINFO, the current filehandle (cfh) is used to identify the file system. If the metadata server is unable to return a single device address, it will return the error NFS4ERR_TOOSMALL. If an invalid device ID is given, the metadata server will respond with NFS4ERR_INVAL. Welch, et al. Expires January 16, 2006 [Page 49] Internet-Draft pNFS Operations July 2005 ERRORS NFS4ERR_BAD_COOKIE NFS4ERR_FHEXPIRED NFS4ERR_INVAL NFS4ERR_TOOSMALL NFS4ERR_UNKNOWN_LAYOUTTYPE 10. Callback Operations 10.1 CB_LAYOUTRECALL SYNOPSIS layout_type, iomode, layoutrecall -> - ARGUMENT enum layoutrecall_type4 { RECALL_FILE = 1, RECALL_FSID = 2 }; union layoutrecall4 switch(layoutrecall_type4 recalltype) { case RECALL_FILE: nfs_fh4 fh; offset4 offset; length4 length; case RECALL_FSID: fsid4 fsid; }; struct CB_LAYOUTRECALLargs { pnfs_layouttype4 layout_type; pnfs_layoutiomode4 iomode; layoutrecall4 layoutrecall; }; RESULT struct CB_LAYOUTRECALLres { nfsstat4 status; }; DESCRIPTION The CB_LAYOUTRECALL operation is used to begin the process of Welch, et al. Expires January 16, 2006 [Page 50] Internet-Draft pNFS Operations July 2005 recalling a layout, a portion thereof, or all layouts pertaining to a particular file system (FSID). If RECALL_FILE is specified, the offset and length fields specify the portion of the layout to be returned. The iomode specifies the set of layouts to be returned. An iomode of ANY specifies that all matching layouts, regardless of iomode, must be returned; otherwise, only layouts that exactly match the iomode must be returned. If RECALL_FSID is specified, the fsid specifies the file system for which any outstanding layouts must be returned. Layouts are returned through the LAYOUTRETURN operation. If RECALL_FILE is specified and the layout byte range specified does not correspond to a valid layout for the file specified by the filehandle, an NFS4ERR_BADLAYOUT is returned. If the byte range overlaps with a layout being held, the portion of the layout represented by the overlap MUST be returned. If a length of all 1s is specified then the layout corresponding to the byte range from "offset" to the end-of-file MUST be returned. If the layout specified is not held by the client, an NFS4ERR_BADLAYOUT error is returned. If the layout type is unknown to the client, then an NFS4ERR_UNKNOWN_LAYOUTTYPE is returned. If a layout exists, but the iomode does not match, then an NFS4ERR_BADIOMODE is returned. IMPLEMENTATION The client should reply to the callback immediately. Replying does not complete the recall except when an error is returned. The recall is not complete until the layout(s) are returned using a LAYOUTRETURN. The client should complete any in-flight I/O operations using the recalled layout(s) before returning it/them via LAYOUTRETURN. If the client has buffered dirty data, it may chose to write it directly to storage before calling LAYOUTRETURN, or to write it later using normal NFSv4 WRITE operations to the metadata server. If a large amount of dirty data is outstanding, the client may issue LAYOUTRETURNs for portions of the layout being recalled; this allows the server to monitor the client's progress and adherence to the callback. ERRORS NFS4ERR_BADLAYOUT NFS4ERR_BADIOMODE NFS4ERR_UNKNOWN_LAYOUTTYPE Welch, et al. Expires January 16, 2006 [Page 51] Internet-Draft pNFS Operations July 2005 [OPEN ISSUE: Should we add a callback type for returning some percentage of the layouts held by a client (something in between all and one)?] 10.2 CB_SIZECHANGED SYNOPSIS fh, size -> - ARGUMENT struct CB_SIZECHANGEDargs { nfs_fh4 fh; length4 size; }; RESULT struct CB_SIZECHANGEDres { nfsstat4 status; }; DESCRIPTION The CB_SIZECHANGED operation is used to notify the client that the size pertaining to the filehandle associated with "fh", has changed. The new size is specified. Upon reception of this notification callback, the client should update its internal size for the file. If the layout being held for the file is of the NFSv4 file layout type, then the size field within that layout should be updated (see Section 5.5.1). For other layout types see Section 3.5.2 for more details. If the handle specified is not one for which the client holds a layout, an NFS4ERR_BADHANDLE error is returned. ERRORS NFS4ERR_BADHANDLE 11. Usage Scenarios This section has a description of common open, close, read, write interactions and how those work with layout delegations. [TODO: this section feels rough and I'm not sure it adds value in its present form.] Welch, et al. Expires January 16, 2006 [Page 52] Internet-Draft pNFS Operations July 2005 11.1 Basic Read Scenario Client does an OPEN to get a file handle. Client does a LAYOUTGET for a range of the file, gets back a layout. Client uses the storage protocol and the layout to access the file. Client returns the layout with LAYOUTRETURN. Client closes stateID and open delegation with CLOSE. This is rather boring as the client is careful to clean up all server state after only a single use of the file. 11.2 Multiple Reads to a File Client does an OPEN to get a file handle. Client does a LAYOUTGET for a range of the file, gets back a layout. Client uses the storage protocol and the layout to access the file. Client closes stateID and with CLOSE. Client does an OPEN to get a file handle. Client finds cached layout associated with file handle. Client uses the storage protocol and the layout to access the file. Client closes stateID and with CLOSE. A bit more interesting as we've saved the LAYOUTGET operation, but we are still doing server round-trips. 11.3 Multiple Reads to a File with Delegations Client does an OPEN to get a file handle and an open delegation. Client does a LAYOUTGET for a range of the file, gets back a layout. Client uses the storage protocol and the layout to access the file. Application does a close(), but client keeps state under the delegation. (time passes) Application does another open(), which client handles under the delegation. Client finds cached layout associated with file handle. Client uses the storage protocol and the layout to access the file. (pattern continues until open delegation and/or layout is recalled) This illustrates the efficiency of combining open delegations and layouts to eliminate interactions with the file server altogether. Of course, we assume the client's operating system is only allowing the local open() to succeed based on the file permissions. The use of layouts does not change anything about the semantics of open delegations. 11.4 Read with existing writers NOTE: This scenario was under some debate, but we have resolved that the server is able to give out overlapping/conflicting layout Welch, et al. Expires January 16, 2006 [Page 53] Internet-Draft pNFS Operations July 2005 information to different clients. In these cases we assume that clients are using an external mechanism such as MPI-IO to synchronize and serialize access to shared data. One can argue that even unsynchronized clients get the same open-to-close consistency semantics as NFS already provides, even when going direct to storage. Client does an OPEN to get an open stateID and open delegation. The file is open for writing elsewhere by different clients and so no open delegation is returned. Client does a LAYOUT get and gets a layout from the server. Client either synchronizes with the writers, or not, and accesses data via the layout and storage protocol. There are no guarantees about when data that is written by the writer is visible to the reader. Once the writer has closed the file and flushed updates to storage, then they are visible to the client. [We should state explicitly that COMMIT and LAYOUTCOMMIT represent explicit points where changes should be visible to other clients.] 11.5 Read with later conflict ClientA does an OPEN to get an open stateID and open delegation. ClientA does a LAYOUTGET for a range of the file, gets back a map and layout stateid. ClientA uses the storage protocol to access the file data. ClientB opens the file for WRITE. File server issues CB_RECALL to ClientA. ClientA issues DELEGRETURN. ClientA continues to use the storage protocol to access file data. If it is accessing data from its cache, it will periodically check that its data is still up-to-date because it has no open delegation. [This is an odd scenario that mixes in open delegations for no real value. Basically this is a "regular writer" being mixed with a pNFS reader. I guess this example shows that no particular semantics are provided during the simultaneous access. If the server so chose, it could also recall the layout with CB_LAYOUTRECALL to force the different clients to serialize at the file server.] 11.6 Basic Write Case Client does an OPEN to get a file handle. Client does a LAYOUTGET for a range of the file, gets back a layout and layout stateid. Client writes to the file using the storage protocol. Client uses LAYOUTCOMMIT to communicate new EOF position. Client does SETATTR to update timestamps. Client does a LAYOUTRETURN. Client does a CLOSE. Again, the boring case where the client cleans up all of its server state by returning the layout. Welch, et al. Expires January 16, 2006 [Page 54] Internet-Draft pNFS Operations July 2005 11.7 Large Write Case Client does an OPEN to get a file handle. (loop.) Client does a LAYOUTGET for a range of the file, gets back a layout and layout stateid. Client writes to the file using the storage protocol. Client fills up the range covered by the layout. Client updates the server with LAYOUTCOMMIT, communicating about new EOF position. Client does SETATTR to update timestamps. Client releases the layout with LAYOUTRELEASE. (end loop.) Client does a CLOSE. 11.8 Create with special layout Client does an OPEN and a SETATTR that specifies a particular layout type using the LAYOUT_HINT attribute. Client gets back an open stateID and file handle. (etc) 12. Layouts and Aggregation This section describes several layout formats in a semi-formal way to provide context for the layout delegations. These definitions will be formalized in other protocols. However, the set of understood types is part of this protocol in order to provide for basic interoperability. The layout descriptions include (deviceID, objectID) tuples that identify some storage object on some storage device. The addressing formation associated with the deviceID is obtained with GETDEVICEINFO. The interpretation of the objectID depends on the storage protocol. The objectID could be a filehandle for an NFSv4 storage device. It could be a OSD object ID for an object server. The layout for a block device generally includes additional block map information to enumerate blocks or extents that are part of the layout. 12.1 Simple Map The data is located on a single storage device. In this case the file server can act as the front end for several storage devices and distribute files among them. Each file is limited in its size and performance characteristics by a single storage device. The simple map consists of (deviceID, objectID). 12.2 Block Map The data is located on a LUN in the SAN. The layout consists of an array of (deviceID, blockID, blocksize) tuples. Alternatively, the blocksize could be specified once to apply to all entries in the layout. Welch, et al. Expires January 16, 2006 [Page 55] Internet-Draft pNFS Operations July 2005 12.3 Striped Map (RAID 0) The data is striped across storage devices. The parameters of the stripe include the number of storage devices (N) and the size of each stripe unit (U). A full stripe of data is N * U bytes. The stripe map consists of an ordered list of (deviceID, objectID) tuples and the parameter value for U. The first stripe unit (the first U bytes) are stored on the first (deviceID, objectID), the second stripe unit on the second (deviceID, objectID) and so forth until the first complete stripe. The data layout then wraps around so that byte (N*U) of the file is stored on the first (deviceID, objectID) in the list, but starting at offset U within that object. The striped layout allows a client to read or write to the component objects in parallel to achieve high bandwidth. The striped map for a block device would be slightly different. The map is an ordered list of (deviceID, blockID, blocksize), where the deviceID is rotated among a set of devices to achieve striping. 12.4 Replicated Map The file data is replicated on N storage devices. The map consists of N (deviceID, objectID) tuples. When data is written using this map, it should be written to N objects in parallel. When data is read, any component object can be used. This map type is controversial because it highlights the issues with error recovery. Those issues get interesting with any scheme that employs redundancy. The handling of errors (e.g., only a subset of replicas get updated) is outside the scope of this protocol extension. Instead, it is a function of the storage protocol and the metadata management protocol. 12.5 Concatenated Map The map consists of an ordered set of N (deviceID, objectID, size) tuples. Each successive tuple describes the next segment of the file. 12.6 Nested Map The nested map is used to compose more complex maps out of simpler ones. The map format is an ordered set of M sub-maps, each submap applies to a byte range within the file and has its own type such as the ones introduced above. Any level of nesting is allowed in order to build up complex aggregation schemes. Welch, et al. Expires January 16, 2006 [Page 56] Internet-Draft pNFS Operations July 2005 13. Issues 13.1 Storage Protocol Negotiation Clients may want to negotiate with the metadata server about their preferred storage protocol, and to find out what storage protocols the server offers. Client can do this by querying the LAYOUT_TYPES file system attribute. They respond by specifying a particular layout type in their LAYOUTGET operation. 13.2 Storage Errors There may be a need for the client to communicate about errors it has when accessing storage directly. The client may do so in a layout type dependent way through the layoutupdate field in LAYOUTCOMMIT. 14. Normative References [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", March 1997. [2] Shepler, S., Callaghan, B., Robinson, D., Thurlow, R., Beame, C., Eisler, M., and D. Noveck, "Network File System (NFS) version 4 Protocol", RFC 3530, April 2003. [3] Weber, R., "Object-Based Storage Device Commands (OSD)", INCITS 400-2004, July 2004, . [4] Gibson, G., "pNFS Problem Statement", July 2004, . Authors' Addresses Brent Welch Panasas, Inc. 6520 Kaiser Drive Fremont, CA 95444 USA Phone: +1-650-608-7770 Email: welch@panasas.com URI: http://www.panasas.com/ Welch, et al. Expires January 16, 2006 [Page 57] Internet-Draft pNFS Operations July 2005 Benny Halevy Panasas, Inc. 1501 Reedsdale St., #400 Pittsburgh, PA 15233 USA Phone: +1-412-323-3500 Email: bhalevy@panasas.com URI: http://www.panasas.com/ Garth Goodson Network Appliance 495 E. Java Dr Sunnyvale, CA 94089 USA Phone: +1-408-822-6847 Email: goodson@netapp.com David L. Black EMC Corporation 176 South Street Hopkinton, MA 01748 USA Phone: +1-508-293-7953 Email: black_david@emc.com Andy Adamson CITI University of Michigan 519 W. William Ann Arbor, MI 48103-4943 USA Phone: +1-734-764-9465 Email: andros@umich.edu Appendix A. Acknowledgments Many members of the pNFS informal working group have helped considerably. The authors would like to thank Gary Grider, Peter Corbett, Dave Noveck, and Peter Honeyman. This work is inspired by the NASD and OSD work done by Garth Gibson. Gary Grider of the national labs (LANL) has been a champion of high-performance parallel I/O. Welch, et al. Expires January 16, 2006 [Page 58] Internet-Draft pNFS Operations July 2005 Intellectual Property Statement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. 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Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Welch, et al. Expires January 16, 2006 [Page 59]