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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   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.

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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.

   Replication of local file access performance on NAS using traditional
   network protocol stacks has proven difficult, not because of protocol
   processing overheads, but because of data copy costs in the network

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   endpoints.  This is especially true since host buses are now often
   the main bottleneck in NAS architectures [MOG03] [CHA+01].

   The External Data Representation [RFC4506] employed beneath NFS and
   the Remote Procedure Call (RPC) [RFC5531] can add more data copies,
   exacerbating the problem.

   Data copy-avoidance designs have not been widely adopted for a
   variety of reasons.  [BRU99] points out that "many copy avoidance
   techniques for network I/O are not applicable or may even backfire if
   applied to file I/O".  Other designs that eliminate unnecessary
   copies, such as [PAI+00], are incompatible with existing APIs and
   therefore force application changes.

   In recent years, an effort to standardize a set of protocols for
   Remote Direct Memory Access (RDMA) over the standard Internet
   Protocol Suite has been chartered [RDDP].  A complete IP-based RDMA
   protocol suite is available in the published Standards Track

   RDMA is a general solution to the problem of CPU overhead incurred
   due to data copies, primarily at the receiver.  Substantial research
   has addressed this and has borne out the efficacy of the approach.
   An overview of this is the "Remote Direct Memory Access (RDMA) over
   IP Problem Statement" [RFC4297].

   In addition to the per-byte savings of offloading data copies, RDMA-
   enabled NICs (RNICS) offload the underlying protocol layers as well
   (e.g., TCP), further reducing CPU overhead due to NAS processing.

1.1.  Background

   The RDDP Problem Statement [RFC4297] asserts:

      High costs associated with copying are an issue primarily for
      large scale systems ... with high bandwidth feeds, usually
      multiprocessors and clusters, that are adversely affected by
      copying overhead.  Examples of such machines include all varieties
      of servers: database servers, storage servers, application servers
      for transaction processing, for e-commerce, and web serving,
      content distribution, video distribution, backups, data mining and
      decision support, and scientific computing.

      Note that such servers almost exclusively service many concurrent
      sessions (transport connections), which, in aggregate, are
      responsible for > 1 Gbits/s of communication.  Nonetheless, the
      cost of copying overhead for a particular load is the same whether
      from few or many sessions.

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   Note that each of the servers listed above could be accessing their
   file data as an NFS client, or as NFS serving the data to such
   clients, or acting as both.

   The CPU overhead of the NFS and TCP/IP protocol stacks (including
   data copies or reduced copy workarounds) becomes a significant matter
   in these clients and servers.  File access using locally attached
   disks imposes relatively low overhead due to the highly optimized I/O
   path and direct memory access afforded to the storage controller.
   This is not the case with NFS, which must pass data to, and
   especially from, the network and network processing stack to the NFS
   stack.  Frequently, data copies are imposed on this transfer; in some
   cases, several such copies are imposed in each direction.

   Copies are potentially encountered in an NFS implementation
   exchanging data to and from user address spaces, within kernel buffer
   caches, in eXternal Data Representation (XDR) marshalling and
   unmarshalling, and within network stacks and network drivers.  Other
   overheads such as serialization among multiple threads of execution
   sharing a single NFS mount point and transport connection are
   additionally encountered.

   Numerous upper-layer protocols achieve extremely high bandwidth and
   low overhead through the use of RDMA.  [MAF+02] shows that the RDMA-
   based Direct Access File System (with a user-level implementation of
   the file system client) can outperform even a zero-copy
   implementation of NFS [CHA+01] [CHA+99] [GAL+99] [KM02].  Also, file
   data access implies the use of large Unequal Loss Protection (ULP)
   messages.  These large messages tend to amortize any increase in
   per-message costs due to the offload of protocol processing incurred
   when using RNICs while gaining the benefits of reduced per-byte
   costs.  Finally, the direct memory addressing afforded by RDMA avoids
   many sources of contention on network resources.

2.  Problem Statement

   The principal performance problem encountered by NFS implementations
   is the CPU overhead required to implement the protocol.  Primary
   among the sources of this overhead is the movement of data from NFS
   protocol messages to its eventual destination in user buffers or
   aligned kernel buffers.  Due to the nature of the RPC and XDR
   protocols, the NFS data payload arrives at arbitrary alignment,
   necessitating a copy at the receiver, and the NFS requests are
   completed in an arbitrary sequence.

   The data copies consume system bus bandwidth and CPU time, reducing
   the available system capacity for applications [RFC4297].  To date,
   achieving zero-copy with NFS has required sophisticated, version-

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   specific "header cracking" hardware and/or extensive platform-
   specific virtual memory mapping tricks.  Such approaches become even
   more difficult for NFS version 4 due to the existence of the COMPOUND
   operation and presence of Kerberos and other security information,
   which further reduce alignment and greatly complicate ULP offload.

   Furthermore, NFS is challenged by high-speed network fabrics such as
   10 Gbits/s Ethernet.  Performing even raw network I/O such as TCP is
   an issue at such speeds with today's hardware.  The problem is
   fundamental in nature and has led the IETF to explore RDMA [RFC4297].

   Zero-copy techniques benefit file protocols extensively, as they
   enable direct user I/O, reduce the overhead of protocol stacks,
   provide perfect alignment into caches, etc.  Many studies have
   already shown the performance benefits of such techniques [SKE+01]
   [DCK+03] [FJNFS] [FJDAFS] [KM02] [MAF+02].

   RDMA is compelling here for another reason; hardware-offloaded
   networking support in itself does not avoid data copies, without
   resorting to implementing part of the NFS protocol in the Network
   Interface Card (NIC).  Support of RDMA by NFS enables the highest
   performance at the architecture level rather than by implementation;
   this enables ubiquitous and interoperable solutions.

   By providing file access performance equivalent to that of local file
   systems, NFS over RDMA will enable applications running on a set of
   client machines to interact through an NFS file system, just as
   applications running on a single machine might interact through a
   local file system.

3.  File Protocol Architecture

   NFS runs as an Open Network Computing (ONC) RPC [RFC5531]
   application.  Being a file access protocol, NFS is very "rich" in
   data content (versus control information).

   NFS messages can range from very small (under 100 bytes) to very
   large (from many kilobytes to a megabyte or more).  They are all
   contained within an RPC message and follow a variable-length RPC
   header.  This layout provides an alignment challenge for the data
   items contained in an NFS call (request) or reply (response) message.

   In addition to the control information in each NFS call or reply
   message, sometimes there are large "chunks" of application file data,
   for example, read and write requests.  With NFS version 4 (due to the
   existence of the COMPOUND operation), there can be several of these
   data chunks interspersed with control information.

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   ONC RPC is a remote procedure call protocol that has been run over a
   variety of transports.  Most implementations today use UDP or TCP.
   RPC messages are defined in terms of an eXternal Data Representation
   (XDR) [RFC4506], which provides a canonical data representation
   across a variety of host architectures.  An XDR data stream is
   conveyed differently on each type of transport.  On UDP, RPC messages
   are encapsulated inside datagrams, while on a TCP byte stream, RPC
   messages are delineated by a record-marking protocol.  An RDMA
   transport also conveys RPC messages in a unique fashion that must be
   fully described if client and server implementations are to

   The RPC transport is responsible for conveying an RPC message from a
   sender to a receiver.  An RPC message is either an RPC call from a
   client to a server, or an RPC reply from the server back to the
   client.  An RPC message contains an RPC call header followed by
   arguments if the message is an RPC call, or an RPC reply header
   followed by results if the message is an RPC reply.  The call header
   contains a transaction ID (XID) followed by the program and procedure
   number as well as a security credential.  An RPC reply header begins
   with an XID that matches that of the RPC call message, followed by a
   security verifier and results.  All data in an RPC message is XDR

   The encoding of XDR data into transport buffers is referred to as
   "marshalling", and the decoding of XDR data contained within
   transport buffers and into destination RPC procedure result buffers,
   is referred to as "unmarshalling".  Therefore, the process of
   marshalling takes place at the sender of any particular message, be
   it an RPC request or an RPC response.  Unmarshalling, of course,
   takes place at the receiver.

   Normally, any bulk data is moved (copied) as a result of the
   unmarshalling process, because the destination address is not known
   until the RPC code receives control and subsequently invokes the XDR
   unmarshalling routine.  In other words, XDR-encoded data is not
   self-describing, and it carries no placement information.  This
   results in a data copy in most NFS implementations.

   One mechanism by which the RPC layer may overcome this is for each
   request to include placement information, to be used for direct
   placement during XDR encode.  This "write chunk" can avoid sending
   bulk data inline in an RPC message and generally results in one or
   more RDMA Write operations.

   Similarly, a "read chunk", where placement information referring to
   bulk data that may be directly fetched via one or more RDMA Read
   operations during XDR decode, may be conveyed.  The "read chunk" will

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   therefore be useful in both RPC calls and replies, while the "write
   chunk" is used solely in replies.

   These "chunks" are the key concept in an existing proposal [RPCRDMA].
   They convey what are effectively pointers to remote memory across the
   network.  They allow cooperating peers to exchange data outside of
   XDR encodings but still use XDR for describing the data to be
   transferred.  And, finally, through use of XDR they maintain a large
   degree of on-the-wire compatibility.

   The central concept of the RDMA transport is to provide the
   additional encoding conventions to convey this placement information
   in transport-specific encoding, and to modify the XDR handling of
   bulk data.

                           Block Diagram

   |         NFS            |            NFS + RDMA             |
   |           Operations / Procedures             |            |
   +-----------------------------------------------+            |
   |                   RPC/XDR                     |            |
   +--------------------------------+--------------+            |
   |       Stream Transport         |      RDMA Transport       |

4.  Sources of Overhead

   Network and file protocol costs can be categorized as follows:

   o  per-byte costs - data touching costs such as checksum or data
      copy.  Today's network interface hardware commonly offloads the
      checksum, which leaves the other major source of per-byte
      overhead, data copy.

   o  per-packet costs - interrupts and lower-layer processing (LLP).
      Today's network interface hardware also commonly coalesce
      interrupts to reduce per-packet costs.

   o  per-message (request or response) costs - LLP and ULP processing.

   Improvement from optimization becomes more important if the overhead
   it targets is a larger share of the total cost.  As other sources of
   overhead, such as the checksumming and interrupt handling above are
   eliminated, the remaining overheads (primarily data copy) loom

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   With copies crossing the bus twice per copy, network processing
   overhead is high whenever network bandwidth is large in comparison to
   CPU and memory bandwidths.  Generally, with today's end-systems, the
   effects are observable at network speeds at or above 1 Gbit/s.

   A common question is whether an increase in CPU processing power
   alleviates the problem of high processing costs of network I/O.  The
   answer is no, it is the memory bandwidth that is the issue.  Faster
   CPUs do not help if the CPU spends most of its time waiting for
   memory [RFC4297].

   TCP offload engine (TOE) technology aims to offload the CPU by moving
   TCP/IP protocol processing to the NIC.  However, TOE technology by
   itself does nothing to avoid necessary data copies within upper-layer
   protocols.  [MOG03] provides a description of the role TOE can play
   in reducing per-packet and per-message costs.  Beyond the offloads
   commonly provided by today's network interface hardware, TOE alone
   (without RDMA) helps in protocol header processing, but this has been
   shown to be a minority component of the total protocol processing
   overhead. [CHA+01]

   Numerous software approaches to the optimization of network
   throughput have been made.  Experience has shown that network I/O
   interacts with other aspects of system processing such as file I/O
   and disk I/O [BRU99] [CHU96].  Zero-copy optimizations based on page
   remapping [CHU96] can be dependent upon machine architecture, and are
   not scalable to multi-processor architectures.  Correct buffer
   alignment and sizing together are needed to optimize the performance
   of zero-copy movement mechanisms [SKE+01].  The NFS message layout
   described above does not facilitate the splitting of headers from
   data nor does it facilitate providing correct data buffer alignment.

4.1.  Savings from TOE

   The expected improvement of TOE specifically for NFS protocol
   processing can be quantified and shown to be fundamentally limited.
   [SHI+03] presents a set of "LAWS" parameters that serve to illustrate
   the issues.  In the TOE case, the copy cost can be viewed as part of
   the application processing "a".  Application processing increases the
   LAWS "gamma", which is shown by the paper to result in a diminished
   benefit for TOE.

   For example, if the overhead is 20% TCP/IP, 30% copy, and 50% real
   application work, then gamma is 80/20 or 4, which means the maximum
   benefit of TOE is 1/gamma, or only 25%.

   For RDMA (with embedded TOE) and the same example, the "overhead" (o)
   offloaded or eliminated is 50% (20% + 30%).  Therefore, in the RDMA

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   case, gamma is 50/50 or 1, and the inverse gives the potential
   benefit of 1 (100%), a factor of two.

                    CPU Overhead Reduction Factor

               No Offload   TCP Offload   RDMA Offload
                  1.00x        1.25x         2.00x

   The analysis in the paper shows that RDMA could improve throughput by
   the same factor of two, even when the host is (just) powerful enough
   to drive the full network bandwidth without RDMA.  It can also be
   shown that the speedup may be higher if network bandwidth grows
   faster than Moore's Law, although the higher benefits will apply to a
   narrow range of applications.

4.2.  Savings from RDMA

   Performance measurements directly comparing an NFS-over-RDMA
   prototype with conventional network-based NFS processing are
   described in [CAL+03].  Comparisons of Read throughput and CPU
   overhead were performed on two types of Gigabit Ethernet adapters,
   one type being a conventional adapter, and another type with RDMA
   capability.  The prototype RDMA protocol performed all transfers via
   RDMA Read.  The NFS layer in the study was measured while performing
   read transfers, varying the transfer size and readahead depth across
   ranges used by typical NFS deployments.

   In these results, conventional network-based throughput was severely
   limited by the client's CPU being saturated at 100% for all
   transfers.  Read throughput reached no more than 60 MBytes/s.

      I/O Type        Size     Read Throughput     CPU Utilization
      Conventional    2 KB         20 MB/s              100%
      Conventional   16 KB         40 MB/s              100%
      Conventional  256 KB         60 MB/s              100%

   However, over RDMA, throughput rose to the theoretical maximum
   throughput of the platform, while saturating the single-CPU system
   only at maximum throughput.

       I/O Type       Size     Read Throughput     CPU Utilization
      RDMA            2 KB         10 MB/s               45%
      RDMA           16 KB         40 MB/s               70%
      RDMA          256 KB        100 MB/s              100%

   The lower relative throughput of the RDMA prototype at the small
   blocksize may be attributable to the RDMA Read imposed by the

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   prototype protocol, which reduced the operation rate since it
   introduces additional latency.  As well, it may reflect the relative
   increase of per-packet setup costs within the DMA portion of the

5.  Application of RDMA to NFS

   Efficient file protocols require efficient data positioning and
   movement.  The client system knows the client memory address where
   the application has data to be written or wants read data deposited.
   The server system knows the server memory address where the local
   file system will accept write data or has data to be read.  Neither
   peer however is aware of the others' data destination in the current
   NFS, RPC, or XDR protocols.  Existing NFS implementations have
   struggled with the performance costs of data copies when using
   traditional Ethernet transports.

   With the onset of faster networks, the network I/O bottleneck will
   worsen.  Fortunately, new transports that support RDMA have emerged.
   RDMA excels at bulk transfer efficiency; it is an efficient way to
   deliver direct data placement and remove a major part of the problem:
   data copies.  RDMA also addresses other overheads, e.g., underlying
   protocol offload, and offers separation of control information from

   The current NFS message layout provides the performance-enhancing
   opportunity for an NFS-over-RDMA protocol that separates the control
   information from data chunks while meeting the alignment needs of
   both.  The data chunks can be copied "directly" between the client
   and server memory addresses above (with a single occurrence on each
   memory bus) while the control information can be passed "inline".
   [RPCRDMA] describes such a protocol.

6.  Conclusions

   NFS version 4 [RFC3530] has been granted "Proposed Standard" status.
   The NFSv4 protocol was developed along several design points,
   important among them: effective operation over wide-area networks,
   including the Internet itself; strong security integrated into the
   protocol; extensive cross-platform interoperability including
   integrated locking semantics compatible with multiple operating
   systems; and (this is key), protocol extension.

   NFS version 4 is an excellent base on which to add the needed
   performance enhancements and improved semantics described above.  The
   minor versioning support defined in NFS version 4 was designed to
   support protocol improvements without disruption to the installed
   base [NFSv4.1].  Evolutionary improvement of the protocol via minor

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   versioning is a conservative and cautious approach to current and
   future problems and shortcomings.

   Many arguments can be made as to the efficacy of the file abstraction
   in meeting the future needs of enterprise data service and the
   Internet.  Fine grained Quality of Service (QoS) policies (e.g., data
   delivery, retention, availability, security, etc.) are high among

   It is vital that the NFS protocol continue to provide these benefits
   to a wide range of applications, without its usefulness being
   compromised by concerns about performance and semantic inadequacies.
   This can reasonably be addressed in the existing NFS protocol
   framework.  A cautious evolutionary improvement of performance and
   semantics allows building on the value already present in the NFS
   protocol, while addressing new requirements that have arisen from the
   application of networking technology.

7.  Security Considerations

   The NFS protocol, in conjunction with its layering on RPC, provides a
   rich and widely interoperable security model to applications and
   systems.  Any layering of NFS-over-RDMA transports must address the
   NFS security requirements, and additionally must ensure that no new
   vulnerabilities are introduced.  For RDMA, the integrity, and any
   privacy, of the data stream are of particular importance.

   The core goals of an NFS-to-RDMA binding are to reduce overhead and
   to enable high performance.  To support these goals while maintaining
   required NFS security protection presents a special challenge.
   Historically, the provision of integrity and privacy have been
   implemented within the RPC layer, and their operation requires local
   processing of messages exchanged with the RPC peer.  This processing
   imposes memory and processing overhead on a per-message basis,
   exactly the overhead that RDMA is designed to avoid.

   Therefore, it is a requirement that the RDMA transport binding
   provide a means to delegate the integrity and privacy processing to
   the RDMA hardware, in order to maintain the high level of performance
   desired from the approach, while simultaneously providing the
   existing highest levels of security required by the NFS protocol.
   This in turn requires a means by which the RPC layer may invoke these
   services from the RDMA provider, and for the NFS layer to negotiate
   their use end-to-end.

   The "Channel Binding" concept [RFC5056] together with "IPsec Channel
   Connection Latching" [BTNSLATCH] provide a means by which the RPC and
   NFS layers may delegate their session protection to the lower RDMA

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   layers.  An extension to the RPCSEC_GSS protocol [RFC5403] may be
   employed to negotiate the use of these bindings, and to establish the
   shared secrets necessary to protect the sessions.

   The protocol described in [RPCRDMA] specifies the use of these
   mechanisms, and they are required to implement the protocol.

   An additional consideration is protection of the integrity and
   privacy of local memory by the RDMA transport itself.  The use of
   RDMA by NFS must not introduce any vulnerabilities to system memory
   contents, or to memory owned by user processes.  These protections
   are provided by the RDMA layer specifications, and specifically their
   security models.  It is required that any RDMA provider used for NFS
   transport be conformant to the requirements of [RFC5042] in order to
   satisfy these protections.

8.  Acknowledgments

   The authors wish to thank Jeff Chase who provided many useful

9.  References

9.1.  Normative 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.

   [RFC5531]   Thurlow, R., "RPC: Remote Procedure Call Protocol
               Specification Version 2", RFC 5531, May 2009.

   [RFC4506]   Eisler, M., Ed., "XDR: External Data Representation
               Standard", STD 67, RFC 4506, May 2006.

   [RFC1813]   Callaghan, B., Pawlowski, B., and P. Staubach, "NFS
               Version 3 Protocol Specification", RFC 1813, June 1995.

   [RFC5403]   Eisler, M., "RPCSEC_GSS Version 2", RFC 5403, February

   [RFC5056]   Williams, N., "On the Use of Channel Bindings to Secure
               Channels", RFC 5056, November 2007.

   [RFC5042]   Pinkerton, J. and E. Deleganes, "Direct Data Placement
               Protocol (DDP) / Remote Direct Memory Access Protocol
               (RDMAP) Security", RFC 5042, October 2007.

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9.2.  Informative References

   [BRU99]     J. Brustoloni, "Interoperation of copy avoidance in
               network and file I/O", in Proc. INFOCOM '99, pages 534-
               542, New York, NY, Mar. 1999., IEEE.  Also available from

   [BTNSLATCH] Williams, N., "IPsec Channels: Connection Latching", Work
               in Progress, November 2008.

   [CAL+03]    B. Callaghan, T. Lingutla-Raj, A. Chiu, P. Staubach, O.
               Asad, "NFS over RDMA", in Proceedings of ACM SIGCOMM
               Summer 2003 NICELI Workshop.

   [CHA+01]    J. S. Chase, A. J. Gallatin, K. G. Yocum, "Endsystem
               optimizations for high-speed TCP", IEEE Communications,
               39(4):68-74, April 2001.

   [CHA+99]    J. S. Chase, D. C. Anderson, A. J. Gallatin, A. R.
               Lebeck, K.  G. Yocum, "Network I/O with Trapeze", in 1999
               Hot Interconnects Symposium, August 1999.

   [CHU96]     H.K. Chu, "Zero-copy TCP in Solaris", Proc. of the USENIX
               1996 Annual Technical Conference, San Diego, CA, January

   [DCK+03]    M. DeBergalis, P. Corbett, S. Kleiman, A. Lent, D.
               Noveck, T.  Talpey, M. Wittle, "The Direct Access File
               System", in Proceedings of 2nd USENIX Conference on File
               and Storage Technologies (FAST '03), San Francisco, CA,
               March 31 - April 2, 2003.

   [FJDAFS]    Fujitsu Prime Software Technologies, "Meet the DAFS
               Performance with DAFS/VI Kernel Implementation using
               cLAN", available from

   [FJNFS]     Fujitsu Prime Software Technologies, "An Adaptation of
               VIA to NFS on Linux", available from
               http://www.pst.fujitsu.com/english/nfs/index.html, 2000.

   [GAL+99]    A. Gallatin, J. Chase, K. Yocum, "Trapeze/IP: TCP/IP at
               Near-Gigabit Speeds", 1999 USENIX Technical Conference
               (Freenix Track), June 1999.

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RFC 5532               NFS RDMA Problem Statement               May 2009

   [KM02]      K. Magoutis, "Design and Implementation of a Direct
               Access File System (DAFS) Kernel Server for FreeBSD", in
               Proceedings of USENIX BSDCon 2002 Conference, San
               Francisco, CA, February 11-14, 2002.

   [MAF+02]    K. Magoutis, S. Addetia, A. Fedorova, M. Seltzer, J.
               Chase, D.  Gallatin, R. Kisley, R. Wickremesinghe, E.
               Gabber, "Structure and Performance of the Direct Access
               File System (DAFS)", in Proceedings of 2002 USENIX Annual
               Technical Conference, Monterey, CA, June 9-14, 2002.

   [MOG03]     J. Mogul, "TCP offload is a dumb idea whose time has
               come", 9th Workshop on Hot Topics in Operating Systems
               (HotOS IX), Lihue, HI, May 2003. USENIX.

   [NFSv4.1]   Shepler, S., Eisler, M., and D. Noveck, "NFSv4 Minor
               Version 1", Work in Progress, September 2008.

   [PAI+00]    V. S. Pai, P. Druschel, W. Zwaenepoel, "IO-Lite: a
               unified I/O buffering and caching system", ACM Trans.
               Computer Systems, 18(1):37-66, Feb. 2000.

   [RDDP]      RDDP Working Group charter,

   [RFC4297]   Romanow, A., Mogul, J., Talpey, T., and S. Bailey,
               "Remote Direct Memory Access (RDMA) over IP Problem
               Statement", RFC 4297, December 2005.

   [RFC1094]   Sun Microsystems, "NFS: Network File System Protocol
               specification", RFC 1094, March 1989.

   [RPCRDMA]   Talpey, T. and B. Callaghan, "Remote Direct Memory Access
               Transport for Remote Procedure Call", Work in Progress,
               April 2008.

   [SHI+03]    P. Shivam, J. Chase, "On the Elusive Benefits of Protocol
               Offload", Proceedings of ACM SIGCOMM Summer 2003 NICELI
               Workshop, also available from

   [SKE+01]    K.-A. Skevik, T. Plagemann, V. Goebel, P. Halvorsen,
               "Evaluation of a Zero-Copy Protocol Implementation", in
               Proceedings of the 27th Euromicro Conference - Multimedia
               and Telecommunications Track (MTT'2001), Warsaw, Poland,
               September 2001.

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RFC 5532               NFS RDMA Problem Statement               May 2009

Authors' Addresses

   Tom Talpey
   170 Whitman St.
   Stow, MA 01775 USA

   Phone: +1 978 821-8577
   EMail: tmtalpey@gmail.com

   Chet Juszczak
   P.O. Box 1467
   Merrimack, NH 03054

   Phone: +1 603 253-6602
   EMail: chetnh@earthlink.net

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