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NFSv4                                                         C. Hellwig
Internet-Draft
Intended status: Informational                             July 08, 2016
Expires: January 9, 2017


          Using the Parallel NFS (pNFS) SCSI Layout with NVMe
              draft-hellwig-nfsv4-scsi-layout-nvme-00.txt

Abstract

   This document explains how to use the Parallel Network File System
   (pNFS) SCSI Layout Type with transports using the NVMe or NVMe over
   Fabrics protocol.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
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   This Internet-Draft will expire on January 9, 2017.

Copyright Notice

   Copyright (c) 2016 IETF Trust and the persons identified as the
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Conventions Used in This Document . . . . . . . . . . . .   2
     1.2.  General Definitions . . . . . . . . . . . . . . . . . . .   2
   2.  SCSI Layout mapping to NVMe . . . . . . . . . . . . . . . . .   3
     2.1.  Volume Identification . . . . . . . . . . . . . . . . . .   3
     2.2.  Client Fencing  . . . . . . . . . . . . . . . . . . . . .   3
     2.3.  Volatile write caches . . . . . . . . . . . . . . . . . .   3
   3.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   5.  Normative References  . . . . . . . . . . . . . . . . . . . .   4
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   4

1.  Introduction

   The pNFS SCSI layout [scsi-layout] is a layout type that allows NFS
   clients to directly perform I/O to block storage devices while
   bypassing the MDS.  It is specified by using concepts from the SCSI
   protocol family for the data path to the storage devices.  This
   documents explains how to access PCI Express, RDMA or Fibre Channel
   devices using the NVM Express protocol [NVME] using the SCSI layout
   type by leveraging the SCSI Translation Reference ([NVME-STLR]).
   This document does not amend the pNFS SCSI layout document in any
   way, instead of explains how to map the SCSI constructs used in the
   pNFS SCSI layout document to NVMe concepts using the NVMe SCSI
   translation reference.

1.1.  Conventions Used in This Document

   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 [RFC2119].

1.2.  General Definitions

   The following definitions are provided for the purpose of providing
   an appropriate context for the reader.

   Client  The "client" is the entity that accesses the NFS server's
      resources.  The client may be an application that contains the
      logic to access the NFS server directly.  The client may also be
      the traditional operating system client that provides remote file
      system services for a set of applications.

   Server  The "server" is the entity responsible for coordinating
      client access to a set of file systems and is identified by a
      server owner.



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2.  SCSI Layout mapping to NVMe

   The SCSI layout definition [scsi-layout] only references few SCSI
   specific concepts directly.  This document uses the NVMe SCSI
   Translation Reference document ([NVME-STLR]) to provide mappings from
   these SCSI concepts to NVM Express ([NVME]) concepts that SHOULD be
   used when using the pNFS SCSI layout with NVMe devices.

   The NVMe SCSI Translation Reference is used to define the NVMe
   command and concepts that SHOULD be used to implement the pNFS SCSI
   layout.  Implementations MAY or MAY not use an actual SCSI to NVMe
   translation layer.

2.1.  Volume Identification

   The SCSI layout uses the Device Identification VPD page (page code
   0x83) from [SPC4] to identify the devices used by a layout.
   Section 6.1.4 of [NVME-STLR] explains how an an implementation SHOULD
   construct a valid Device Identification VPD page based on the NVMe
   Identify data.  Only NVMe devices that support either the EUI64 or
   NGUID value in the Identify Namespace data SHOULD be used as storage
   devices for the pNFS SCSI layout, as the methods based on the Serial
   Number for legacy devices might not be suitable for unique addressing
   needs.

2.2.  Client Fencing

   The SCSI layout uses Persistent Reservations to provide client
   fencing.  For this both the MDS and the Clients have to register a
   key with the storage device, and the MDS has to create a reservation
   on the storage device.  Section 6.7 of [NVME-STLR] contains a full
   mapping of the required PERSISTENT RESERVE IN and PERSISTENT RESERVE
   OUT SCSI command to NVMe commands which SHOULD be used when using
   NVMe devices as storage devices for the pNFS SCSI layout.

2.3.  Volatile write caches

   The equivalent of the WCE bit in the Caching Mode Page in [SBC3] is
   the Write Cache Enable field in the NVMe Get Features command, see
   Section 6.3.3.2 of [NVME-STLR].  If a write cache is enable on a NVMe
   device used as a storage device for the pNFS SCSI layout, the MDS
   must ensure to use the NVMe FLUSH command to flush the volatile write
   cache.








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3.  Security Considerations

   Since no protocol changes are proposed here, no security
   considerations apply.

4.  IANA Considerations

   The document does not require any actions by IANA.

5.  Normative References

   [NVME]     NVM Express, Inc., "NVM Express Revision 1.2.1", July
              2016.

   [NVME-STLR]
              NVM Express, Inc., "NVM Express: SCSI Translation
              Reference Revision 1.5", June 2015.

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

   [SBC3]     INCITS Technical Committee T10, "SCSI Block Commands-3",
              ANSI INCITS INCITS 514-2014, ISO/IEC 14776-323, 2014.

   [SPC4]     INCITS Technical Committee T10, "SCSI Primary Commands-4",
              ANSI INCITS 513-2015, 2015.

   [scsi-layout]
              Hellwig, C., "Parallel NFS (pNFS) SCSI Layout", June 2016.

Author's Address

   Christoph Hellwig

   Email: hch@lst.de
















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