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.
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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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