Internet-Draft Brent Callaghan Expires: August 2005 Tom Talpey Document: draft-ietf-nfsv4-nfsdirect-01 February, 2005 NFS Direct Data Placement Status of this Memo By submitting this Internet-Draft, I certify that any applicable patent or other IPR claims of which I am aware have been disclosed, or will be disclosed, and any of which I become aware will be dis- closed, in accordance with RFC 3668. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other docu- ments at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Inter- net-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. Copyright Notice Copyright (C) The Internet Society (2005). All Rights Reserved. Abstract The RDMA transport for ONC RPC provides direct data placement for NFS data. Direct data placement not only reduces the amount of data that needs to be copied in an NFS call, but allows much of the data Expires: August 2005 Callaghan and Talpey [Page 1]
Internet-Draft NFS Direct Data Placement February 2005 movement over the network to be implemented in RDMA hardware. This draft describes the use of direct data placement by means of server- initiated RDMA operations into client-supplied buffers in a Chunk list for implementations of NFS versions 2, 3, and 4 over an RDMA transport. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. RDMA Read List . . . . . . . . . . . . . . . . . . . . . . . 2 3. RDMA Write List . . . . . . . . . . . . . . . . . . . . . . 3 4. NFS Versions 2 and 3 Mapping . . . . . . . . . . . . . . . . 4 5. NFS Version 4 Mapping . . . . . . . . . . . . . . . . . . . 5 6. Security . . . . . . . . . . . . . . . . . . . . . . . . . . 7 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . 7 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7 9. Normative References . . . . . . . . . . . . . . . . . . . . 7 10. Informative References . . . . . . . . . . . . . . . . . . 8 11. Authors' Addresses . . . . . . . . . . . . . . . . . . . . 9 12. Full Copyright Statement . . . . . . . . . . . . . . . . . 9 Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 10 1. Introduction The RDMA Transport for ONC RPC [RPCRDMA] allows an RPC client application to post buffers in a Chunk list for specific arguments and results from an RPC call. The RDMA transport header conveys this list of client buffer addresses to the server where the application can associate them with client data and use RDMA operations to transfer the results directly to and from the posted buffers on the client. The client and server must agree on a consistent mapping of posted buffers to RPC. This document details the mapping for each version of the NFS protocol. 2. RDMA Read List The RDMA Read list, in the RDMA transport header, allows an RPC client to marshall RPC call data selectively. Large chunks of data, such as the file data of an NFS WRITE request, can be referenced from the RDMA Read list and be moved efficiently and direct-placed by an RDMA READ operation initiated by the server. Expires: August 2005 Callaghan and Talpey [Page 2]
Internet-Draft NFS Direct Data Placement February 2005 The process of identifying these chunks for the RDMA Read list can be implemented entirely within the RPC layer. It is transparent to the upper-level protocol, such as NFS. For instance, the file data portion of an NFS WRITE request can be selected as an RDMA "chunk" within the XDR marshalling code of RPC based on a size criterion, independently of the NFS protocol layer. The XDR unmarshalling on the receiving system can identify the correspondence between Read chunks and protocol elements via the XDR position value encoded in the Read chunk entry. However, the implementation of the RDMA Write list requires some help from the NFS protocol layer to identify the candidate chunks. Since there is no simple XDR position value to unambiguously label Write chunks, both client and server must agree on a mapping of write chunk entries to protocol elements. 3. RDMA Write List The RDMA Write list, in the RDMA transport header, allows the client to post one or more buffers into which the server will RDMA Write designated result chunks directly. If the client sends a null write list, then results from the RPC call will be returned as either an in-line reply, as chunks in an RDMA Read list of server-posted buffers, or in a client-posted reply buffer. Each posted buffer in a Write list is represented as an array of memory segments. This allows the client some flexibility in submitting discontiguous memory segments into which the server will scatter the result. Each segment is described by a triplet consisting of the segment handle or steering tag (STag), segment length, and memory address or offset. struct xdr_rdma_segment { uint32 handle; /* Registered memory handle */ uint32 length; /* Length of the chunk in bytes */ uint64 offset; /* Chunk virtual address or offset */ }; struct xdr_write_chunk { struct xdr_rdma_segment target<>; }; Expires: August 2005 Callaghan and Talpey [Page 3]
Internet-Draft NFS Direct Data Placement February 2005 struct xdr_write_list { struct xdr_write_chunk entry; struct xdr_write_list *next; }; The sum of the segment lengths yields the total size of the buffer, which must be large enough to accept the result. If the buffer is too small, the server must return an XDR encode error. The server must return the result data for a posted buffer by progressively filling its segments, perhaps leaving some trailing segments unfilled or partially full if the size of the result is less than the total size of the buffer segments. The server returns the RDMA Write list to the client with the segment length fields overwritten to indicate the amount of data RDMA Written to each segment. Results returned by direct placement must not be returned by other methods, e.g. by read chunk list or in-line. The RDMA Write list allows the client to provide multiple result buffers - each buffer must map to a specific result in the reply. The NFS client and server implementations must agree on the mapping of results to buffers for each RPC procedure. The following sections describe this mapping for versions of the NFS protocol. Through the use of RDMA Write lists in NFS requests, it is not necessary to employ the RDMA Read lists in the NFS replies, as described in the RPC/RDMA protocol. This enables more efficient operation, by avoiding the need for the server to expose buffers for RDMA, and also avoiding "RDMA_DONE" messages. 4. NFS Versions 2 and 3 Mapping A single RDMA Write list entry may be posted by the client to receive either the opaque file data from a READ request or the pathname from a READLINK request. The server will ignore a Write list for any other NFS procedure, as well as any Write list entries beyond the first in the list. Similarly, a single RDMA Read list entry may be posted by the client to supply the opaque file data for a WRITE request or the pathname for a SYMLINK request. The server will ignore any Read list for other NFS procedures, as well as additional Read list entries beyond the first in the list. Because there are no NFS version 2 or 3 requests that transfer bulk Expires: August 2005 Callaghan and Talpey [Page 4]
Internet-Draft NFS Direct Data Placement February 2005 data in both directions, it is not necessary to post requests containing both Write and Read lists. Any unneeded Read or Write lists are ignored by the server. In the case where the outgoing request or expected incoming reply is larger than the maximum size supported on the connection, it is possible for the RPC layer to post the entire message or result in a special "RDMA_NOMSG" message type which is transferred entirely by RDMA. This is implemented in RPC, below NFS and therefore has no effect on the message contents. Non-RDMA (inline) WRITE transfers may optionally employ the "RDMA_MSGP" padding method described in the RPC/RDMA protocol, if the appropriate value for the server is known to the client. Padding allows the opaque file data to arrive at the server in an aligned fashion, which may improve server performance. The NFS version 2 and 3 protocols are frequently limited in practice to requests containing less than or equal to 8 kilobytes and 32 kilobytes of data, respectively. In these cases, it is often practical to support basic operation without employing a configuration exchange as discussed in [RPCRDMA]. The server can post buffers large enough to receive the largest possible incoming message (approximately 12KB/36KB would be vastly sufficient in the above cases), and the client can post buffers large enough to receive replies based on the "rsize" it is using to the server. Flow control is handled dynamically by the RPC RDMA protocol, and write padding is optional and therefore may remain unused. Alternatively, if the server is administratively configured to values appropriate for all its clients, the same assurance of interoperability within the domain can be made. The use of a configuration protocol with NFS v2 and v3 is therefore optional. Employing a configuration exchange may allow some advantage to server resource management through accurately sizing buffers, enabling the server to know exactly how many RDMA Reads may be in progress at once on the client connection, and enabling client write padding which may be desirable for certain servers when RDMA Read is impractical. 5. NFS Version 4 Mapping This specification applies to the first minor version of NFS version 4 (NFSv4.0) and any subsequent minor versions that do not override Expires: August 2005 Callaghan and Talpey [Page 5]
Internet-Draft NFS Direct Data Placement February 2005 this mapping. The Write list will be considered only for the COMPOUND procedure. This procedure returns results from a sequence of operations. Only the opaque file data from an NFS READ operation, and the pathname from a READLINK operation will utilize entries from the Write list. If there is no Write list, i.e. the list is null, then any READ or READLINK operations in the COMPOUND must return their data either in- line or via RDMA READ (using the Read list). The first entry in the Write list must be used by the first READ or READLINK in the request. The next Write list entry by the by the next READ or READLINK, and so on. If there are more READ or READLINK operations than Write list entries, then any remaining operations must return their results in-line or via the Read list. If a Write list entry is presented, then the corresponding READ or READLINK must return its data via an RDMA WRITE to the buffer indicated by the Write list entry. If the Write list entry has zero RDMA segments, or if the total size of the segments is zero, then the corresponding READ or READLINK operation must return its result in- line or via Read list. The following example shows an RDMA Write list with three posted buffers A, B, and C. The designated operations in the compound request, READ and READLINK, consume the posted buffers by writing their results back to each buffer. RDMA Write list: A --> B --> C Compound request: PUTFH LOOKUP READ PUTFH LOOKUP READLINK PUTFH LOOKUP READ | | | v v v A B C Expires: August 2005 Callaghan and Talpey [Page 6]
Internet-Draft NFS Direct Data Placement February 2005 If the client does not want to have the READLINK result returned directly, then it provides a zero length array of segment triplets for buffer B or sets the values in the segment triplet for buffer B to zeros so that the READLINK result will be returned in-line. The situation is similar for RDMA Read lists and applies to the NFSv4.0 WRITE and SYMLINK procedures as for v3. Additionally, inline segments too large to fit in posted buffers may be transferred in special "RDMA_NOMSG" messages. Non-RDMA (inline) WRITE transfers may optionally employ the "RDMA_MSGP" padding method described in the RPC/RDMA protocol, if the appropriate value for the server is known to the client. Padding allows the opaque file data to arrive at the server in an aligned fashion, which may improve server performance. In order to ensure accurate alignment for all data, it is likely that the client will restrict its use of optional padding to COMPOUND requests containing only a single WRITE operation. Unlike NFS versions 2 and 3, the maximum size of an NFS version 4 COMPOUND is unbounded, even when RDMA chunks are in use. While it might appear that a configuration protocol exchange (as described in [RPCRDMA]) would help, in fact the layering issues involved in building COMPOUNDs by NFS make such a mechanism unworkable. Instead, an extension to NFS version 4 supporting a more comprehensive exchange of upper layer (NFSv4) parameters is proposed in [NFSSESSIONS]. This proposal also addresses other use of the sizes, such as in the server's response cache. 6. Security The RDMA transport for ONC RPC supports RPCSEC_GSS security as well as link-level security. The use of RDMA Write to return RPC results does not affect ONC RPC security. 7. IANA Considerations NFS use of direct data placement introduces no new IANA considerations. Expires: August 2005 Callaghan and Talpey [Page 7]
Internet-Draft NFS Direct Data Placement February 2005 8. Acknowledgements The authors would like to thank Dave Noveck and Chet Juszczak for their contributions to this document. 9. Normative References [RFC1831] R. Srinivasan, "RPC: Remote Procedure Call Protocol Specification Version 2", Standards Track RFC, http://www.ietf.org/rfc/rfc1831.txt [RFC1832] R. Srinivasan, "XDR: External Data Representation Standard", Standards Track RFC, http://www.ietf.org/rfc/rfc1832.txt [RFC1094] "NFS: Network File System Protocol Specification", (NFS version 2) Informational RFC, http://www.ietf.org/rfc/rfc1094.txt [RFC1813] B. Callaghan, B. Pawlowski, P. Staubach, "NFS Version 3 Protocol Specification", Informational RFC, http://www.ietf.org/rfc/rfc1813.txt [RFC3530] S. Shepler, B. Callaghan, D. Robinson, R. Thurlow, C. Beame, M. Eisler, D. Noveck, "NFS version 4 Protocol", Standards Track RFC, http://www.ietf.org/rfc/rfc3530.txt 10. Informative References [RPCRDMA] B. Callaghan, T. Talpey, "RDMA Transport for ONC RPC" Internet Draft Work in Progress, http://www.ietf.org/internet-drafts/ Expires: August 2005 Callaghan and Talpey [Page 8]
Internet-Draft NFS Direct Data Placement February 2005 draft-ietf-nfsv4-rpcrdma-01.txt [NFSSESSIONS] T. Talpey, S. Shepler, J. Bauman, "NFSv4 Session Extensions" Internet Draft Work in Progress, http://www.ietf.org/internet-drafts/ draft-ietf-nfsv4-sess-01.txt 11. Authors' Addresses Brent Callaghan 1614 Montalto Dr. Mountain View, California 94040 USA Phone: +1 650 968 2333 EMail: brent.callaghan@gmail.com Tom Talpey Network Appliance, Inc. 375 Totten Pond Road Waltham, MA 02451 USA Phone: +1 781 768 5329 EMail: thomas.talpey@netapp.com 12. Full Copyright Statement Copyright (C) The Internet Society (2005). This document is sub- ject to the rights, licenses and restrictions contained in BCP 78 and except as set forth therein, the authors retain all their rights. This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REP- RESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Expires: August 2005 Callaghan and Talpey [Page 9]
Internet-Draft NFS Direct Data Placement February 2005 Intellectual Property The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC docu- ments can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this speci- fication can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf- ipr@ietf.org. Acknowledgement Funding for the RFC Editor function is currently provided by the Internet Society. Expires: August 2005 Callaghan and Talpey [Page 10]
