NFSv4 C. Hellwig
Internet-Draft June 04, 2017
Intended status: Informational
Expires: December 6, 2017
Using the Parallel NFS (pNFS) SCSI Layout with NVMe
draft-hellwig-nfsv4-scsi-layout-nvme-01.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 Small Computer System Interface (SCSI) layout [RFC8154] 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 [RFC8154] 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 pNFS 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] lists ways to build SCSI Device
Identification descriptors from NVMe Identify data. To be used as
storage devices for the pNFS SCSI layout, NVMe devices MUST support
either the EUI64 or NGUID value in the Identify Namespace data, as
the methods based on the Serial Number for legacy devices might not
be suitable for unique addressing needs and thus MUST NOT be used.
If possible NVMe devices uses as storage devices for the pNFS SCSI
layout SHOULD support the NGUID value as it is the larger identifier.
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. One
important difference between SCSI and NVMe Persistent Reservations is
that NVMe reservation keys always apply to all controllers used by a
host (as indicated by the NVMe HOSTID). This behavior is somewhat
similar to setting the ALL_TG_PT bit when registering a SCSI
Reservation key, but actually guaranteed to work reliably.
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
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must ensure to use the NVMe FLUSH command to flush the volatile write
cache.
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 1.3", May 2017.
[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.
[RFC8154] Hellwig, C., "Parallel NFS (pNFS) Small Computer System
Interface (SCSI) Layout", May 2017.
[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.
Author's Address
Christoph Hellwig
Email: hch@lst.de
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