Internet Engineering Task Force M.E. Eisler, Ed.
Internet-Draft NetApp
Intended status: Informational October 2009
Expires: April 02, 2010

Requirements for NFSv4.2


This document proposes requirements for NFSv4.2.

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Table of Contents

1. Introduction

NFSv4.1 [I-D.ietf-nfsv4-minorversion1] is an approved specification. The NFSv4 [RFC3530] community has indicated a desire to continue innovating NFS, and specifically via a new minor version of NFSv4, namely NFSv4.2. The desire for future innovation is primarily driven by two trends in the storage industry:

Secondarily, innovation is being driver by the trend to stronger compliance with information management. In addition, as might be expected with a complex protocol like NFSv4.1, implementation experience has shown that minor changes to the protocol would be useful to improve the end user experience.

This document proposes requirements along these four themes, and attempts to strike the balance between stating the problem and proposing solutions. With respect to the latter, some thinking among the NFS community has taken place, and a future revision of this document will reference embodiments of such thinking.

1.1. Requirements Language

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 RFC 2119 [RFC2119].

2. Efficiency and Utilization Requirements

2.1. Capacity

Despite the capacity of magnetic disk continuing to increase at exponential rates, the storage industry is under pressure to make the storage of data increasingly more efficient, so that more data can be stored. The driver for this counter-intuitive demand is that disk access times are not improving any where near as quickly as capacities. The industry has responded to this by increasing data density by limiting the number of times a unique pattern of data is stored in a storage device. For example some storage devices support de-duplication. When storing two files, a sorage device might compare them for shared patterns of data, and store the pattern just once, and setting reference counts on the blocks of the unique pattern to two. With de-duplication the number of times a storage device has to read a particular pattern just once, thus improving average access time.

For a file access protocol like NFS, there are several implied requirements for addressing this capacity efficiency trend:

2.2. Network Bandwidth and Processing

The computation capabilities of processors continues at an exponential rate. However, as noted previous, disk access times are not tracking this. In addition, while network bandwidth is exponentially increasing, unlike disk capacities and processor bandwidth, the improvement is not seen on a 1-2 year cycle, but is closer to a 10 year cycle. This means that there is often a discontinuity between the processing capabilities of NFS clients, and the speed at which they can extract data from an NFS server. For some use cases, much of the data that is read by one client from an NFS server also needs to be read by another client. Re-reading this data is waste of the network bandwidth and processing of the NFS server. This same observation has driven the creation of peer-to-peer content distribution protocols, where data is directly read from peers rather than servers. It is apparent that a similar technique could be used to offload primary storage.

The pNFS protocol distributes the I/O to a set of files across a cluster of of data servers. arguably, its primary value is in balancing load across storage devices, especially when it can leverage a back end file system or storage cluster with automatic load balancing capabilities. In NFSv4.1, no consideration was given to metadata. Metadata is critical to several workloads, to the point that as defined in NFSv4.1, pNFS will not not offer much value in those cases. The load balancing capabilities of pNFS need to be brought to metadata.

From an end user perspective, the operations he performs on a file include creating, reading, writing, deleting, and copying. NFSv4 has operations for all but the last. While file copy has been proposed for NFS in the past, it was always rejected because of the lack of APIs on operating environments to send a copy operation. The IT trend toward virtualization via hypervisors has changed the picture. The use of a copy operation will save network bandwidth on the client and server, and where the server supports it, intra-server fle copy can potentially be zero copy.

2.3. Flash Memory Requirements

Flash memory is rapidly filling the wide gap between expensive but fast Dynamic Random Access Memory (DRAM) and inexpensive but cheap magnetic disk. The cost per bit of flash is between DRAM and disk. The access time pet bit of flash is between DRAM and disk. This has resulted in cost per File access Operation Per Second (FOPS) of flash exceeding DRAM and disk. Flash can be easily added as another storage medium to NFS servers, and this does not require a change to the NFS protocol. However, the value of flash's superior FOPS is best realized when flash is closest to the application, i.e. on the NFS client. One approach would be to forgo the use of network storage and de-evolve back to Direct Attached Storage (DAS). However, this would require that data protection value that exists in modern storage devices be brought into DAS, and this is not always convenient or cost effective. A less traumatic way to leverage the full FOPS of flash would be for NFSv4 clients to leverage flash for caching of data.

Today NFSv4 supports whole file delegations for enabling caching. Such a granularity is useful for applications like user home directories where there is little file sharing. However, NFS is used for many more workloads, which include file sharing. In these workloads, files are shared, whereas individual blocks might not be. This drives a requirement for sub-file caching.

3. Compliance

New regulations for the IT industry limit who can view what data. NFSv4 has Access Control Lists (ACLs), but the ACL can be changed by the nominal file owner. In practice, the end user that owns the file (essentially, has the right to delete the file or give permissions to other users), is not the legal owner of the file. The legal owner of the file wants to control not just who can access the file, but who they can pass the content of the file to. The IT industry has addressed this need in the past with notion of security labeling. Labels are attached to devices, files, users, applications, network connections, etc. When the labels of two objects match, data can be transferred from one to another. For example a label called "Secret" on a file results in only users with a "Secret" security clearance being allowed to view the file, despite what the ACL says.

To attach a label on a file requires that it be created atomically with the file, which means that a new RECOMMENDED attribute for a security label is needed.

4. Incremental Improvements

Implementation experience with NFSv4.1 and related protocols, such as SMB2, has shown a number of areas where the protocol can be improved.

5. IANA Considerations


6. Security Considerations


7. References

7.1. Normative References

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

7.2. Informative References

[RFC3530] Shepler, S., Callaghan, B., Robinson, D., Thurlow, R., Beame, C., Eisler, M. and D. Noveck, "Network File System (NFS) version 4 Protocol", RFC 3530, April 2003.
[I-D.ietf-nfsv4-minorversion1] Shepler, S, Eisler, M and D Noveck, "NFS Version 4 Minor Version 1", Internet-Draft draft-ietf-nfsv4-minorversion1-29, December 2008.

Author's Address

Michael Eisler (editor) NetApp 5765 Chase Point Circle Colorado Springs, CO 80919 US Phone: +1 719 599 8759 EMail: