Parallel NFS (pNFS) Flexible File Layout
RFC 8435

Document Type RFC - Proposed Standard (August 2018; No errata)
Last updated 2018-08-24
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Internet Engineering Task Force (IETF)                         B. Halevy
Request for Comments: 8435
Category: Standards Track                                      T. Haynes
ISSN: 2070-1721                                              Hammerspace
                                                             August 2018

                Parallel NFS (pNFS) Flexible File Layout

Abstract

   Parallel NFS (pNFS) allows a separation between the metadata (onto a
   metadata server) and data (onto a storage device) for a file.  The
   flexible file layout type is defined in this document as an extension
   to pNFS that allows the use of storage devices that require only a
   limited degree of interaction with the metadata server and use
   already-existing protocols.  Client-side mirroring is also added to
   provide replication of files.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc8435.

Copyright Notice

   Copyright (c) 2018 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Halevy & Haynes              Standards Track                    [Page 1]
RFC 8435                pNFS Flexible File Layout            August 2018

Table of Contents

   1. Introduction ....................................................3
      1.1. Definitions ................................................4
      1.2. Requirements Language ......................................6
   2. Coupling of Storage Devices .....................................6
      2.1. LAYOUTCOMMIT ...............................................7
      2.2. Fencing Clients from the Storage Device ....................7
           2.2.1. Implementation Notes for Synthetic uids/gids ........8
           2.2.2. Example of Using Synthetic uids/gids ................9
      2.3. State and Locking Models ..................................10
           2.3.1. Loosely Coupled Locking Model ......................11
           2.3.2. Tightly Coupled Locking Model ......................12
   3. XDR Description of the Flexible File Layout Type ...............13
      3.1. Code Components Licensing Notice ..........................14
   4. Device Addressing and Discovery ................................16
      4.1. ff_device_addr4 ...........................................16
      4.2. Storage Device Multipathing ...............................17
   5. Flexible File Layout Type ......................................18
      5.1. ff_layout4 ................................................19
           5.1.1. Error Codes from LAYOUTGET .........................23
           5.1.2. Client Interactions with FF_FLAGS_NO_IO_THRU_MDS ...23
      5.2. LAYOUTCOMMIT ..............................................24
      5.3. Interactions between Devices and Layouts ..................24
      5.4. Handling Version Errors ...................................24
   6. Striping via Sparse Mapping ....................................25
   7. Recovering from Client I/O Errors ..............................25
   8. Mirroring ......................................................26
      8.1. Selecting a Mirror ........................................26
      8.2. Writing to Mirrors ........................................27
           8.2.1. Single Storage Device Updates Mirrors ..............27
           8.2.2. Client Updates All Mirrors .........................27
           8.2.3. Handling Write Errors ..............................28
           8.2.4. Handling Write COMMITs .............................28
      8.3. Metadata Server Resilvering of the File ...................29
   9. Flexible File Layout Type Return ...............................29
      9.1. I/O Error Reporting .......................................30
           9.1.1. ff_ioerr4 ..........................................30
      9.2. Layout Usage Statistics ...................................31
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