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Parallel NFS (pNFS) Block Disk Protection
RFC 6688

Document Type RFC - Proposed Standard (July 2012)
Updates RFC 5663
Authors David L. Black , Jason Glasgow , Sorin Faibish
Last updated 2015-10-14
RFC stream Internet Engineering Task Force (IETF)
Additional resources Mailing list discussion
IESG Responsible AD Martin Stiemerling
Send notices to (None)
RFC 6688
Internet Engineering Task Force (IETF)                     D. Black, Ed.
Request for Comments: 6688                               EMC Corporation
Updates: 5663                                                 J. Glasgow
Category: Standards Track                                         Google
ISSN: 2070-1721                                               S. Faibish
                                                         EMC Corporation
                                                               July 2012

               Parallel NFS (pNFS) Block Disk Protection


   Parallel NFS (pNFS) extends the Network File System version 4 (NFSv4)
   to enable direct client access to file data on storage devices and
   bypass the NFSv4 server.  This can increase both performance and
   parallelism, but it requires additional client functionality, some of
   which depends upon the type of storage used.  The pNFS specification
   for block storage (RFC 5663) describes how clients can identify the
   volumes used for pNFS, but this mechanism requires communication with
   the NFSv4 server.  This document updates RFC 5663 to add a mechanism
   that enables identification of block storage devices used by pNFS
   file systems without communicating with the server.  This enables
   clients to control access to pNFS block devices when the client
   initially boots, as opposed to waiting until the client can
   communicate with the NFSv4 server.

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 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at

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RFC 6688               pNFS Block Disk Protection              July 2012

Copyright Notice

   Copyright (c) 2012 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
   ( 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.

Table of Contents

   1. Introduction ....................................................3
   2. Conventions Used in This Document ...............................4
   3. GPT Partition Table Entry .......................................4
   4. Security Considerations .........................................5
   5. References ......................................................5
      5.1. Normative References .......................................5
      5.2. Informative References .....................................6
   6. Acknowledgements.................................................6

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RFC 6688               pNFS Block Disk Protection              July 2012

1.  Introduction

   Figure 1 shows the overall architecture of a Parallel NFS (pNFS)

       |+-----------+                                 +-----------+
       ||+-----------+                                |           |
       |||           |       NFSv4.1 + pNFS           |           |
       +||  Clients  |<------------------------------>|    MDS    |
        +|           |                                |           |
         +-----------+                                |           |
              |||                                     +-----------+
              |||                                           |
              |||                                           |
              ||| Storage        +-----------+              |
              ||| Protocol       |+-----------+             |
              ||+----------------||+-----------+  Control   |
              |+-----------------|||           |  Protocol  |
              +------------------+||  Storage  |------------+
                                  +|  Devices  |

                       Figure 1.  pNFS Architecture

   In this document, "storage device" is used as a general term for a
   data server and/or storage server for any pNFS layout type.  The
   MetaData Server (MDS) is the NFSv4 server that provides pNFS layouts
   to clients and handles operations on file metadata (e.g., names and

   For the pNFS block protocol as specified in [RFC5663], client
   identification of pNFS storage devices requires contacting the MDS to
   obtain device signature information.  It is not possible for a pNFS
   client to reliably identify pNFS block storage devices without
   contacting the MDS, because the device signature location and
   contents may vary among devices and servers; both device signature
   location and contents are determined by the MDS, not the client.

   Typical operating system (OS) boot functionality scans and activates
   block devices (e.g., Small Computer System Interface (SCSI)) before
   activating the NFS client (including pNFS functionality).  This
   sequence of operations creates a window of time during which the
   client OS may modify a pNFS block device without contacting the
   server (e.g., by attempting to mount or initialize a local physical
   filesystem).  This document specifies an identification mechanism for
   pNFS block storage devices that can be used by an OS implementation
   to remove this window of vulnerability.

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   Many storage area network (SAN) storage systems provide quasi-static
   access control mechanisms (e.g., Logical Unit Number (LUN) mapping
   and/or masking) that operate at the granularity of individual hosts.
   While it is feasible to use such mechanisms to remove this window
   (e.g., by only enabling a client to access pNFS block storage devices
   after the client has contacted the responsible MDS), such usage is
   undesirable and potentially problematic.  This is because the storage
   access control mechanisms are quasi-static; they are typically
   configured once to allow client access to the block pNFS storage
   devices and not reconfigured dynamically (e.g., based on crashes and
   reboots).  Block storage access controls can be changed to respond to
   unusual circumstances (e.g., to fence [remove access from] an
   uncooperative pNFS client), but should not be used as part of routine
   client operations (e.g., reboot).  A different mechanism is needed.

   This document specifies an entry in the GUID (Globally Unique
   Identifier) partition table (GPT) that can be used by a pNFS server
   to label pNFS storage devices.  This GPT entry is intended for shared
   pNFS storage devices that are accessible to pNFS clients and servers,
   and that may be accessible to other hosts or systems.  This entry
   enables pNFS clients, as well as other hosts and systems, to avoid
   accessing pNFS storage devices via means other than pNFS.

2.  Conventions Used in This Document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC2119].

3.  GPT Partition Table Entry

   The following mechanism enables pNFS clients to identify pNFS block
   storage devices without contacting the server:

      -  Each block storage device dedicated to pNFS includes a GUID
         partition table (GPT) [GPT].

      -  The pNFS block storage partitions are identified in the GPT
         with GUID e5b72a69-23e5-4b4d-b176-16532674fc34, which has been
         generated for this purpose.  GPT GUID usage is well understood
         and implemented.  This document provides a definition for this
         GUID and its usage.  A central registration mechanism does not
         exist for GPT GUIDs, or GUIDs in general, by design; see

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RFC 6688               pNFS Block Disk Protection              July 2012

   This mechanism enables an operating system to prevent non-pNFS access
   to pNFS block storage immediately upon boot.  Servers that support
   pNFS block layouts SHOULD use the GPT and this GUID for all pNFS
   block storage devices.

   A pNFS client operating system that supports block layouts SHOULD
   recognize this GUID and SHOULD use its presence to prevent data
   access to pNFS block devices until a layout that includes the device
   is received from the MDS.

   Data stored on pNFS block layout storage devices can be better
   protected by incorporating checks for this GUID into other hosts and
   systems that do not support pNFS block layouts.  If pNFS block
   storage devices are presented to such hosts or systems by mistake,
   the check for presence of this GUID can be used to prevent writes
   that could otherwise corrupt stored pNFS data.

   Many current operating system versions support the GPT [GPT-W].

4. Security Considerations

   The pNFS block layout security considerations in [RFC5663] apply to
   this document.

   The security considerations in [RFC4122] apply to the GUID specified
   in this document.

5. References

5.1. Normative References

   [GPT]      Unified EFI Forum, "Unified Extensible Firmware Interface
              Specification", Version 2.3.1, Errata A, Section 5.3,
              September 2011, available from

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC5663]  Black, D., Fridella, S., and J. Glasgow, "Parallel NFS
              (pNFS) Block/Volume Layout", RFC 5663, January 2010.

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RFC 6688               pNFS Block Disk Protection              July 2012

5.2. Informative References

   [GPT-W]    Wikipedia, "GUID Partition Table", July 2012,

   [RFC4122]  Leach, P., Mealling, M., and R. Salz, "A Universally
              Unique IDentifier (UUID) URN Namespace", RFC 4122, July

6.  Acknowledgements

   This document was produced by the IETF NFSv4 Working Group.  Review
   comments from members of the working group improved this document and
   are gratefully acknowledged.  The authors would like to thank Tom
   Talpey, and members of the IESG for helpful comments on this
   document, and also Alex Burlyga for providing an appropriate
   reference for the format of the GPT.

Authors' Addresses

   David L. Black (editor)
   EMC Corporation
   176 South Street
   Hopkinton, MA 01748
   Phone: +1 (508) 293-7953

   Jason Glasgow
   5 Cambridge Center, Floors 3-6
   Cambridge, MA 02142
   Phone: +1 (617) 575-1599

   Sorin Faibish
   EMC Corporation
   228 South Street
   Hopkinton, MA 01748
   Phone: +1 (508) 305-8545

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