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Network File System (NFS) Remote Direct Memory Access (RDMA) Problem Statement
RFC 5532

Network Working Group                                          T. Talpey
Request for Comments: 5532                                   C. Juszczak
Category: Informational                                         May 2009

     Network File System (NFS) Remote Direct Memory Access (RDMA)
                           Problem Statement

Status of This Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

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Abstract

   This document addresses enabling the use of Remote Direct Memory
   Access (RDMA) by the Network File System (NFS) protocols.  NFS
   implementations historically incur significant overhead due to data
   copies on end-host systems, as well as other processing overhead.
   This document explores the potential benefits of RDMA to these
   implementations and evaluates the reasons why RDMA is especially
   well-suited to NFS and network file protocols in general.

Talpey & Juszczak            Informational                      [Page 1]
RFC 5532               NFS RDMA Problem Statement               May 2009

Table of Contents

   1. Introduction ....................................................2
      1.1. Background .................................................3
   2. Problem Statement ...............................................4
   3. File Protocol Architecture ......................................5
   4. Sources of Overhead .............................................7
      4.1. Savings from TOE ...........................................8
      4.2. Savings from RDMA ..........................................9
   5. Application of RDMA to NFS .....................................10
   6. Conclusions ....................................................10
   7. Security Considerations ........................................11
   8. Acknowledgments ................................................12
   9. References .....................................................12
      9.1. Normative References ......................................12
      9.2. Informative References ....................................13

1.  Introduction

   The Network File System (NFS) protocol (as described in [RFC1094],
   [RFC1813], and [RFC3530]) is one of several remote file access
   protocols used in the class of processing architecture sometimes
   called Network-Attached Storage (NAS).

   Historically, remote file access has proven to be a convenient,
   cost-effective way to share information over a network, a concept
   proven over time by the popularity of the NFS protocol.  However,
   there are issues in such a deployment.

   As compared to a local (direct-attached) file access architecture,
   NFS removes the overhead of managing the local on-disk file system
   state and its metadata, but interposes at least a transport network
   and two network endpoints between an application process and the
   files it is accessing.  To date, this trade-off has usually resulted
   in a net performance loss as a result of reduced bandwidth, increased
   application server CPU utilization, and other overheads.

   Several classes of applications, including those directly supporting
   enterprise activities in high-performance domains such as database
   applications and shared clusters, have therefore encountered issues
   with moving to NFS architectures.  While this has been due
   principally to the performance costs of NFS versus direct-attached
   files, other reasons are relevant, such as the lack of strong
   consistency guarantees being provided by NFS implementations.

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