[Docs] [txt|pdf|xml|html] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits]
Versions: 00 01 02
Network File System Version 4 C. Lever
Internet-Draft Oracle
Intended status: Standards Track 4 July 2020
Expires: 5 January 2021
Network File System (NFS) Upper-Layer Binding To RPC-Over-RDMA Version 2
draft-ietf-nfsv4-nfs-ulb-v2-02
Abstract
This document specifies Upper-Layer Bindings of Network File System
(NFS) protocol versions to RPC-over-RDMA version 2.
Note
Discussion of this draft takes place on the NFSv4 working group
mailing list (nfsv4@ietf.org), which is archived at
https://mailarchive.ietf.org/arch/browse/nfsv4/. Working Group
information can be found at https://datatracker.ietf.org/wg/nfsv4/
about/.
This note is to be removed before publishing as an RFC.
The source for this draft is maintained in GitHub. Suggested changes
can be submitted as pull requests at https://github.com/chucklever/
i-d-nfs-ulb-v2. Instructions are on that page as well.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 5 January 2021.
Lever Expires 5 January 2021 [Page 1]
Internet-Draft NFS on RPC-Over-RDMA V2 July 2020
Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
extracted from this document must include Simplified BSD License text
as described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3
3. Reply Size Estimation . . . . . . . . . . . . . . . . . . . . 4
4. Upper-Layer Binding for NFS Versions 2 and 3 . . . . . . . . 4
4.1. Reply Size Estimation . . . . . . . . . . . . . . . . . . 4
4.2. RPC Binding Considerations . . . . . . . . . . . . . . . 5
4.3. Transport Considerations . . . . . . . . . . . . . . . . 5
5. Upper-Layer Bindings for NFS Version 2 and 3 Auxiliary
Protocols . . . . . . . . . . . . . . . . . . . . . . . . 6
5.1. MOUNT, NLM, and NSM Protocols . . . . . . . . . . . . . . 6
5.2. NFSACL Protocol . . . . . . . . . . . . . . . . . . . . . 7
6. Upper-Layer Binding For NFS Version 4 . . . . . . . . . . . . 7
6.1. DDP-Eligibility . . . . . . . . . . . . . . . . . . . . . 7
6.2. Reply Size Estimation . . . . . . . . . . . . . . . . . . 8
6.3. RPC Binding Considerations . . . . . . . . . . . . . . . 9
6.4. NFS COMPOUND Requests . . . . . . . . . . . . . . . . . . 9
6.5. NFS Callback Requests . . . . . . . . . . . . . . . . . . 12
6.6. Session-Related Considerations . . . . . . . . . . . . . 13
6.7. Transport Considerations . . . . . . . . . . . . . . . . 14
7. Extending NFS Upper-Layer Bindings . . . . . . . . . . . . . 15
8. Security Considerations . . . . . . . . . . . . . . . . . . . 16
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 16
10.1. Normative References . . . . . . . . . . . . . . . . . . 16
10.2. Informative References . . . . . . . . . . . . . . . . . 17
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 18
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 18
Lever Expires 5 January 2021 [Page 2]
Internet-Draft NFS on RPC-Over-RDMA V2 July 2020
1. Introduction
The RPC-over-RDMA version 2 transport may employ direct data
placement to convey data payloads associated with RPC transactions
[I-D.ietf-nfsv4-rpcrdma-version-two]. RPC client and server
implementations using RPC-over-RDMA version 2 must agree which XDR
data items and RPC procedures are eligible to use direct data
placement (DDP) to ensure successful interoperation.
An Upper-Layer Binding specifies this agreement for one or more
versions of one RPC program. Other operational details, such as RPC
binding assignments, pairing Write chunks with result data items, and
reply size estimation, are also specified by this Binding.
This document contains material required of Upper-Layer Bindings, as
specified in [I-D.ietf-nfsv4-rpcrdma-version-two], for the following
NFS protocol versions:
* NFS version 2 [RFC1094]
* NFS version 3 [RFC1813]
* NFS version 4.0 [RFC7530]
* NFS version 4.1 [RFC5661]
* NFS version 4.2 [RFC7862]
The current document also provides Upper-Layer Bindings for auxiliary
protocols used with NFS versions 2 and 3 (see Section 5).
This document assumes the reader is already familiar with concepts
and terminology defined in [I-D.ietf-nfsv4-rpcrdma-version-two] and
the documents it references.
2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
Lever Expires 5 January 2021 [Page 3]
Internet-Draft NFS on RPC-Over-RDMA V2 July 2020
3. Reply Size Estimation
During the construction of each RPC Call message, a Requester is
responsible for allocating appropriate resources for receiving the
corresponding Reply message. If the Requester expects that the RPC
Reply message could be larger than its inline threshold, it MAY
provide Write chunks wherein the Responder can place results and
Reply chunks wherein the Responder can place the reply's Payload
stream. A message continuation facility is also available in RPC-
over-RDMA version 2 to convey RPC messages that are larger than the
transport's inline threshold.
4. Upper-Layer Binding for NFS Versions 2 and 3
The Upper-Layer Binding specification in this section applies to NFS
version 2 [RFC1094] and NFS version 3 [RFC1813]. For brevity, in
this document, a "Legacy NFS client" refers to an NFS client using
version 2 or version 3 of the NFS RPC program (100003) to communicate
with an NFS server. Likewise, a "Legacy NFS server" is an NFS server
communicating with clients using NFS version 2 or NFS version 3.
The following XDR data items in NFS versions 2 and 3 are DDP-
eligible:
* The opaque file data argument in the NFS WRITE procedure
* The pathname argument in the NFS SYMLINK procedure
* The opaque file data result in the NFS READ procedure
* The pathname result in the NFS READLINK procedure
All other argument or result data items in NFS versions 2 and 3 are
not DDP-eligible.
Whether or not an NFS operation is considered non-idempotent, a
transport error might not indicate whether the server has processed
the arguments of the RPC Call, or whether the server has accessed or
modified client memory associated with that RPC.
4.1. Reply Size Estimation
A Legacy NFS client determines the maximum reply size for each
operation using the criteria outlined in Section 3.
Lever Expires 5 January 2021 [Page 4]
Internet-Draft NFS on RPC-Over-RDMA V2 July 2020
4.2. RPC Binding Considerations
Legacy NFS servers traditionally listen for clients on UDP and TCP
port 2049. Additionally, they register these ports with a local
portmapper service [RFC1833].
A Legacy NFS server supporting RPC-over-RDMA version 2 and
registering itself with the RPC portmapper MAY choose an arbitrary
port, or MAY use the alternative well-known port number for its RPC-
over-RDMA service (see Section 9). The chosen port MAY be registered
with the RPC portmapper using the netids assigned in
[I-D.ietf-nfsv4-rpcrdma-version-two].
4.3. Transport Considerations
Legacy NFS client implementations often rely on a transport-layer
keep-alive mechanism to detect when a legacy server has become
unresponsive. When an NFS server is no longer responsive, client-
side keep-alive terminates the connection, which in turn triggers
reconnection and retransmission of outstanding RPC transactions.
4.3.1. Keep-Alive
Some RDMA transports (such as the Reliable Connected QP type on
InfiniBand) have no keep-alive mechanism. Without a disconnect or
new RPC traffic, such connections can remain alive long after an NFS
server has become unresponsive or unreachable. Once an NFS client
has consumed all available RPC-over-RDMA version 2 credits on that
transport connection, it awaits a reply indefinitely before sending
another RPC request.
Legacy NFS clients SHOULD reserve one RPC-over-RDMA version 2 credit
to use for periodic server or connection health assessment. Either
peer can use this credit to drive an RPC request on an otherwise idle
connection, triggering either an affirmative server response or a
connection termination.
4.3.2. Replay Detection
Legacy NFS servers typically employ request replay detection to
reduce the risk of data corruption that could result when an NFS
client retransmits a non-idempotent NFS request. A legacy NFS server
can send a cached response when a replay is detected, rather than
executing the request again. Replay detection is not perfect, but it
is usually adequate.
Lever Expires 5 January 2021 [Page 5]
Internet-Draft NFS on RPC-Over-RDMA V2 July 2020
For legacy NFS servers, replay detection commonly utilizes heuristic
indicators such as the IP address of the NFS client, the source port
of the connection, the transaction ID of the request, and the
contents of the request's RPC and upper-layer protocol headers. In
short, replay detection is typically based on a connection tuple and
the request's XID. A legacy NFS client is careful to re-use the same
source port, if practical, when reconnecting so that legacy NFS
servers are better able to detect retransmissions.
However, a legacy NFS client operating over an RDMA transport has no
control over connection source ports. It is almost certain that an
RPC request that is retransmitted on a new connection can never be
detected as a replay if the legacy NFS server includes the connection
source port in its replay detection heuristics.
Therefore a legacy NFS server using an RDMA transport should never
use a legacy NFS client connection's source port as part of its NFS
request replay detection mechanism.
5. Upper-Layer Bindings for NFS Version 2 and 3 Auxiliary Protocols
Storage administrators typically deploy NFS versions 2 and 3 with
several other protocols, sometimes referred to as "NFS auxiliary
protocols." These are distinct RPC programs that define procedures
that are not part of the NFS RPC program (100003). The Upper-Layer
Bindings in this section apply to:
* Versions 2 and 3 of the MOUNT RPC program (100005) [RFC1813]
* Versions 1, 3, and 4 of the NLM RPC program (100021) [RFC1813]
* Version 1 of the NSM RPC program (100024), described in Chapter 11
of [XNFS]
* Version 1 of the NFSACL RPC program (100227), which does not have
a public definition. NFSACL is treated in this document as a de
facto standard, as there are several interoperating
implementations.
5.1. MOUNT, NLM, and NSM Protocols
Historically, NFS/RDMA implementations have chosen to convey the
MOUNT, NLM, and NSM protocols via TCP. A legacy NFS server
implementation MUST provide support for these protocols via TCP to
enable interoperation of these protocols when NFS/RDMA is in use.
Lever Expires 5 January 2021 [Page 6]
Internet-Draft NFS on RPC-Over-RDMA V2 July 2020
5.2. NFSACL Protocol
Often legacy clients and servers that support the NFSACL RPC program
convey NFSACL procedures on the same connection as the NFS RPC
program (100003). Utilizing the same connection obviates the need
for separate rpcbind queries to discover server support for this RPC
program.
ACLs are typically small, but even large ACLs must be encoded and
decoded to some degree before being made available to users. Thus no
data item in this Upper-Layer Protocol is DDP-eligible.
For procedures whose replies do not include an ACL object, the size
of a reply is determined directly from the NFSACL RPC program's XDR
definition. Legacy client implementations should choose a maximum
size for ACLs based on internal limits.
6. Upper-Layer Binding For NFS Version 4
The Upper-Layer Binding specification in this section applies to
versions of the NFS RPC program defined in NFS version 4.0 [RFC7530]
NFS version 4.1 [RFC5661] and NFS version 4.2 [RFC7862].
6.1. DDP-Eligibility
Only the following XDR data items in the COMPOUND procedure of all
NFS version 4 minor versions are DDP-eligible:
* The opaque data field in the WRITE4args structure
* The linkdata field of the NF4LNK arm in the createtype4 union
* The opaque data field in the READ4resok structure
* The linkdata field in the READLINK4resok structure
6.1.1. The NFSv4.2 READ_PLUS operation
NFS version 4.2 introduces an enhanced READ operation called
READ_PLUS [RFC7862]. READ_PLUS enables an NFS server to perform
inline data reduction of READ results so that the returned READ data
is more compact.
In a READ_PLUS result, returned file content appears as a list of one
or more of the following items:
* Regular data content: the same as the result of a traditional READ
operation.
Lever Expires 5 January 2021 [Page 7]
Internet-Draft NFS on RPC-Over-RDMA V2 July 2020
* Unallocated space in a file: where no data has yet been written or
previously-written data has been removed via a hole-punch
operation.
* A counted pattern.
Upon receipt of a READ_PLUS result, an NFSv4.2 client expands the
returned list into a preferred local representation of the original
file content.
Before receiving that result, an NFSv4.2 client typically does not
know how the file's content is organized on the NFS server. Thus it
is not possible to predict the size or structure of a READ_PLUS Reply
in advance. The use of direct data placement is therefore
challenging.
A READ_PLUS content list containing more than one segment of regular
file data could be conveyed using multiple Write chunks, but only if
the client knows in advance where those chunks appear in the Reply
Payload stream. Moreover, the usual benefits of hardware-assisted
data placement are entirely waived if the client-side transport must
parse the result of each read I/O.
Therefore this Upper Layer Binding does not make any element of an
NFSv4.2 READ_PLUS Reply DDP-eligible. Further, this Upper Layer
Binding recommends that implementers disable the use of the READ_PLUS
operation on NFS/RDMA mount points.
6.2. Reply Size Estimation
Within NFS version 4, there are certain variable-length result data
items whose maximum size cannot be estimated by clients reliably
because there is no protocol-specified size limit on these result
arrays. These include:
* The attrlist4 field
* Fields containing ACLs such as fattr4_acl, fattr4_dacl, and
fattr4_sacl
* Fields in the fs_locations4 and fs_locations_info4 data structures
* Fields which pertain to pNFS layout metadata, such as loc_body,
loh_body, da_addr_body, lou_body, lrf_body, fattr_layout_types,
and fs_layout_types
Lever Expires 5 January 2021 [Page 8]
Internet-Draft NFS on RPC-Over-RDMA V2 July 2020
6.2.1. Reply Size Estimation for Minor Version 0
The NFS version 4.0 protocol itself does not impose any bound on the
size of NFS calls or replies.
Some of the data items enumerated in Section 6.2 (in particular, the
items related to ACLs and fs_locations) make it difficult to predict
the maximum size of NFS version 4.0 replies that interrogate
variable-length fattr4 attributes. Client implementations might rely
upon internal architectural limits to constrain the reply size, but
such limits are not always guaranteed to be reliable.
When an NFS version 4.0 client expects an especially sizeable fattr4
result, it can provide a Reply chunk to enable that server to return
that result via explicit RDMA. An NFS version 4.0 client can use
short Reply chunk retry when an NFS COMPOUND containing a GETATTR
operation encounters a transport error.
6.2.2. Reply Size Estimation for Minor Version 1 and Newer
In NFS version 4.1 and newer minor versions, the csa_fore_chan_attrs
argument of the CREATE_SESSION operation contains a
ca_maxresponsesize field. The value in this field can be taken as
the absolute maximum size of replies generated by an NFS version 4.1
server.
An NFS version 4 client can use this value in cases where it is not
possible to estimate a reply size upper bound precisely. In
practice, objects such as ACLs, named attributes, layout bodies, and
security labels are much smaller than this maximum.
6.3. RPC Binding Considerations
NFS version 4 servers are required to listen on TCP port 2049, and
they are not required to register with a rpcbind service [RFC7530].
Therefore, an NFS version 4 server supporting RPC-over-RDMA version 2
MUST use the alternative well-known port number for its RPC-over-RDMA
service (see Section 9 Clients SHOULD connect to this well-known port
without consulting the RPC portmapper (as for NFS version 4 on TCP
transports).
6.4. NFS COMPOUND Requests
Lever Expires 5 January 2021 [Page 9]
Internet-Draft NFS on RPC-Over-RDMA V2 July 2020
6.4.1. Multiple DDP-eligible Data Items
An NFS version 4 COMPOUND procedure can contain more than one
operation that carries a DDP-eligible data item. An NFS version 4
client provides XDR Position values in each Read chunk to
disambiguate which chunk is associated with which argument data item.
However, NFS version 4 server and client implementations must agree
in advance on how to pair Write chunks with returned result data
items.
In the following lists, a "READ operation" refers to any NFS version
4 operation that has a DDP-eligible result data item. An NFS version
4 client applies the mechanism specified in Section 4.3.2 of
[I-D.ietf-nfsv4-rpcrdma-version-two] is applied to this class of
operations as follows:
* If an NFS version 4 client wishes all DDP-eligible items in an NFS
reply to be conveyed inline, it leaves the Write list empty.
An NFS version 4 server applies that mechanism as follows:
* The first chunk in the Write list MUST be used by the first READ
operation in an NFS version 4 COMPOUND procedure. The next Write
chunk is used by the next READ operation, and so on.
* If an NFS version 4 client has provided a matching non-empty Write
chunk, then the corresponding READ operation MUST return its DDP-
eligible data item using that chunk.
* If an NFS version 4 client has provided an empty matching Write
chunk, then the corresponding READ operation MUST return all of
its result data items inline.
* If a READ operation returns a union arm which does not contain a
DDP-eligible result, and the NFS version 4 client has provided a
matching non-empty Write chunk, an NFS version 4 server MUST
return an empty Write chunk in that Write list position.
* If there are more READ operations than Write chunks, then
remaining NFS Read operations in an NFS version 4 COMPOUND that
have no matching Write chunk MUST return their results inline.
Lever Expires 5 January 2021 [Page 10]
Internet-Draft NFS on RPC-Over-RDMA V2 July 2020
6.4.2. Chunk List Complexity
The RPC-over-RDMA version 2 protocol does not place any limit on the
number of chunks or segments that may appear in Read or Write lists.
However, for various reasons, NFS version 4 server implementations
often have practical limits on the number of chunks or segments they
can process in a single RPC transaction conveyed via RPC-over-RDMA
version 2.
These implementation limits are especially important when Kerberos
integrity or privacy is in use [RFC7861]. GSS services increase the
size of credential material in RPC headers, potentially requiring the
use of a Long message, which increases the complexity of chunk lists
independent of the particular NFS version 4 COMPOUND being conveyed.
In the absence of explicit knowledge of the server's limits, NFS
version 4 clients SHOULD follow the prescriptions listed below when
constructing RPC-over-RDMA version 2 messages. NFS version 4 servers
MUST accept and process all such requests.
* The Read list can contain either a Position-Zero Read chunk, one
Read chunk with a non-zero Position, or both.
* The Write list can contain no more than one Write chunk.
* Any chunk can contain up to sixteen RDMA segments.
NFS version 4 clients wishing to send more complex chunk lists can
provide configuration interfaces to bound the complexity of NFS
version 4 COMPOUNDs, limit the number of elements in scatter-gather
operations, and avoid other sources of chunk overruns at the
receiving peer.
If an NFS version 4 server receives an RPC request via RPC-over-RDMA
version 2 that it cannot process due to chunk list complexity limits,
it SHOULD return one of the following responses to the client:
* A problem is detected by the transport layer while parsing the
transport header in an RPC Call message. The server responds with
an RDMA2_ERROR message with the err field set to ERR_CHUNK.
* A problem is detected during XDR decoding of the RPC Call message
while the RPC layer reassembles the call's XDR stream. The server
responds with an RPC reply with its "reply_stat" field set to
MSG_ACCEPTED and its "accept_stat" field set to GARBAGE_ARGS.
Lever Expires 5 January 2021 [Page 11]
Internet-Draft NFS on RPC-Over-RDMA V2 July 2020
After receiving one of these errors, an NFS version 4 client SHOULD
NOT retransmit the failing request, as the result would be the same
error. It SHOULD immediately terminate the RPC transaction
associated with the XID in the reply.
6.4.3. NFS Version 4 COMPOUND Example
The following example shows a Write list with three Write chunks, A,
B, and C. The NFS version 4 server consumes the provided Write
chunks by writing the results of the designated operations in the
compound request (READ and READLINK) back to each chunk.
Write list:
A --> B --> C
NFS version 4 COMPOUND request:
PUTFH LOOKUP READ PUTFH LOOKUP READLINK PUTFH LOOKUP READ
| | |
v v v
A B C
If the NFS version 4 client does not want to have the READLINK result
returned via RDMA, it provides an empty Write chunk for buffer B to
indicate that the READLINK result must be returned inline.
6.5. NFS Callback Requests
The NFS version 4 family of protocols support server-initiated
callbacks to notify NFS version 4 clients of events such as recalled
delegations.
6.5.1. NFS Version 4.0 Callback
NFS version 4.0 implementations typically employ a separate TCP
connection to handle callback operations, even when the forward
channel uses an RPC-over-RDMA version 2 transport.
No operation in the NFS version 4.0 callback RPC program conveys a
data payload of significant size. Therefore, no XDR data items in
this RPC program is DDP-eligible.
A CB_RECALL reply is small and fixed in size. The CB_GETATTR reply
contains a variable-length fattr4 data item. See Section 6.2.1 for a
discussion of reply size prediction for this data item.
Lever Expires 5 January 2021 [Page 12]
Internet-Draft NFS on RPC-Over-RDMA V2 July 2020
An NFS version 4.0 client advertises netids and ad hoc port addresses
for contacting its NFS version 4.0 callback service using the
SETCLIENTID operation.
6.5.2. NFS Version 4.1 Callback
In NFS version 4.1 and newer minor versions, callback operations may
appear on the same connection as is used for NFS version 4 forward
channel client requests. NFS version 4 clients and servers MUST use
the approach described in [RFC8167] to convey backchannel operations
on an RPC-over-RDMA version 2 transport.
The csa_back_chan_attrs argument of the CREATE_SESSION operation
contains a ca_maxresponsesize field. The value in this field is the
absolute maximum size of backchannel replies generated by a replying
NFS version 4 client.
There are no DDP-eligible data items in callback procedures defined
in NFS version 4.1 or NFS version 4.2. However, some callback
operations, such as messages that convey device ID information, can
be sizeable. A sender can use Message Continuation or a Long message
in this situation.
When an NFS version 4.1 client can support Long Calls in its
backchannel, it reports a backchannel ca_maxrequestsize that is
larger than the connection's inline thresholds. Otherwise, an NFS
version 4 server MUST use only Short messages to convey backchannel
operations.
6.6. Session-Related Considerations
The presence of an NFS version 4 session (as defined in [RFC5661])
does not effect the operation of RPC-over-RDMA version 2. None of
the operations introduced to support NFS sessions (e.g., the SEQUENCE
operation) contain DDP-eligible data items. There is no need to
match the number of session slots with the number of available RPC-
over-RDMA version 2 credits.
However, there are a few new cases where an RPC transaction can fail.
For example, a Requester might receive, in response to an RPC
request, an RDMA2_ERROR message with a rdma_err value of ERR_CHUNK.
These situations are not different from existing RPC errors, which an
NFS session implementation can already handle for other transport
types. Moreover, there might be no SEQUENCE result available to the
Requester to distinguish whether failure occurred before or after the
Responder executed the requested operations.
Lever Expires 5 January 2021 [Page 13]
Internet-Draft NFS on RPC-Over-RDMA V2 July 2020
When a transport error occurs (e.g., an RDMA2_ERROR type message is
received), the Requester proceeds, as usual, to match the incoming
XID value to a waiting RPC Call. The Requester terminates the RPC
transaction and reports the result status to the RPC consumer. The
Requester's session implementation then determines the session ID and
slot for the failed request and performs slot recovery to make that
slot usable again. Otherwise, that slot could be rendered
permanently unavailable.
When an NFS session is not present (for example, when NFS version 4.0
is in use), a transport error does not indicate whether the server
has processed the arguments of the RPC Call, or whether the server
has accessed or modified client memory associated with that RPC.
6.7. Transport Considerations
6.7.1. Congestion Avoidance
Section 3.1 of [RFC7530] states:
Where an NFS version 4 implementation supports operation over the
IP network protocol, the supported transport layer between NFS and
IP MUST be an IETF standardized transport protocol that is
specified to avoid network congestion; such transports include TCP
and the Stream Control Transmission Protocol (SCTP).
Section 2.9.1 of [RFC5661] further states:
Even if NFS version 4.1 is used over a non-IP network protocol, it
is RECOMMENDED that the transport support congestion control.
It is permissible for a connectionless transport to be used under
NFS version 4.1; however, reliable and in-order delivery of data
combined with congestion control by the connectionless transport
is REQUIRED. As a consequence, UDP by itself MUST NOT be used as
an NFS version 4.1 transport.
RPC-over-RDMA version 2 utilizes only RDMA Reliable Connected QP type
connections [I-D.ietf-nfsv4-rpcrdma-version-two]. RDMA Reliable
Connected QPs are reliable, connection-oriented transports that
guarantee in-order delivery, meeting all the above requirements.
Lever Expires 5 January 2021 [Page 14]
Internet-Draft NFS on RPC-Over-RDMA V2 July 2020
6.7.2. Retransmission and Keep-alive
NFS version 4 client implementations often rely on a transport-layer
keep-alive mechanism to detect when an NFS version 4 server has
become unresponsive. When an NFS server is no longer responsive,
client-side keep-alive terminates the connection, which in turn
triggers reconnection and RPC retransmission.
Some RDMA transports (such as the Reliable Connected QP type on
InfiniBand) have no keep-alive mechanism. Without a disconnect or
new RPC traffic, such connections can remain alive long after an NFS
server has become unresponsive. Once an NFS client has consumed all
available RPC-over-RDMA version 2 credits on that transport
connection, it indefinitely awaits a reply before sending another RPC
request.
NFS version 4 clients SHOULD reserve one RPC-over-RDMA version 2
credit to use for periodic server or connection health assessment.
Either peer can use this credit to drive an RPC request on an
otherwise idle connection, triggering either a quick affirmative
server response or immediate connection termination.
In addition to network partition and request loss scenarios, RPC-
over-RDMA version 2 transport connections can be terminated when a
Transport header is malformed, Reply messages exceed receive
resources, or when too many RPC-over-RDMA messages are sent at once.
In such cases:
* If a transport error occurs (e.g., an RDMA2_ERROR type message is
received) before the disconnect or instead of a disconnect, the
Requester MUST respond to that error as prescribed by the
specification of the RPC transport. Then the NFS version 4 rules
for handling retransmission apply.
* If there is a transport disconnect and the Responder has provided
no other response for a request, then only the NFS version 4 rules
for handling retransmission apply.
7. Extending NFS Upper-Layer Bindings
RPC programs such as NFS are required to have an Upper-Layer Binding
specification to interoperate on RPC-over-RDMA version 2 transports
[I-D.ietf-nfsv4-rpcrdma-version-two]. Via standards action, the
Upper-Layer Binding specified in this document can be extended to
cover versions of the NFS version 4 protocol specified after NFS
version 4 minor version 2, or to cover separately published
extensions to an existing NFS version 4 minor version, as described
in [RFC8178].
Lever Expires 5 January 2021 [Page 15]
Internet-Draft NFS on RPC-Over-RDMA V2 July 2020
8. Security Considerations
RPC-over-RDMA version 2 supports all RPC security models, including
RPCSEC_GSS security and transport-level security [RFC7861]. The
choice of what Direct Data Placement mechanism to convey RPC argument
and results does not affect this since it changes only the method of
data transfer. Because the current document defines only the binding
of the NFS protocols atop [I-D.ietf-nfsv4-rpcrdma-version-two], all
relevant security considerations are, therefore, described at that
layer.
9. IANA Considerations
The use of direct data placement in NFS introduces a need for an
additional port number assignment for networks that share traditional
UDP and TCP port spaces with RDMA services. The iWARP protocol is
such an example [RFC5040] [RFC5041].
For this purpose, the current document specifies a set of transport
protocol port number assignments. IANA has assigned the following
ports for NFS/RDMA in the IANA port registry, according to the
guidelines described in [RFC6335].
nfsrdma 20049/tcp Network File System (NFS) over RDMA
nfsrdma 20049/udp Network File System (NFS) over RDMA
nfsrdma 20049/sctp Network File System (NFS) over RDMA
The current document should be added as a reference for the nfsrdma
port assignments. The current document does not alter these
assignments.
10. References
10.1. Normative References
[I-D.ietf-nfsv4-rpcrdma-version-two]
Lever, C. and D. Noveck, "RPC-over-RDMA Version 2
Protocol", Work in Progress, Internet-Draft, draft-ietf-
nfsv4-rpcrdma-version-two-02, 3 July 2020,
<https://tools.ietf.org/html/draft-ietf-nfsv4-rpcrdma-
version-two-02>.
[RFC1833] Srinivasan, R., "Binding Protocols for ONC RPC Version 2",
RFC 1833, DOI 10.17487/RFC1833, August 1995,
<https://www.rfc-editor.org/info/rfc1833>.
Lever Expires 5 January 2021 [Page 16]
Internet-Draft NFS on RPC-Over-RDMA V2 July 2020
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC5661] Shepler, S., Ed., Eisler, M., Ed., and D. Noveck, Ed.,
"Network File System (NFS) Version 4 Minor Version 1
Protocol", RFC 5661, DOI 10.17487/RFC5661, January 2010,
<https://www.rfc-editor.org/info/rfc5661>.
[RFC6335] Cotton, M., Eggert, L., Touch, J., Westerlund, M., and S.
Cheshire, "Internet Assigned Numbers Authority (IANA)
Procedures for the Management of the Service Name and
Transport Protocol Port Number Registry", BCP 165,
RFC 6335, DOI 10.17487/RFC6335, August 2011,
<https://www.rfc-editor.org/info/rfc6335>.
[RFC7530] Haynes, T., Ed. and D. Noveck, Ed., "Network File System
(NFS) Version 4 Protocol", RFC 7530, DOI 10.17487/RFC7530,
March 2015, <https://www.rfc-editor.org/info/rfc7530>.
[RFC7861] Adamson, A. and N. Williams, "Remote Procedure Call (RPC)
Security Version 3", RFC 7861, DOI 10.17487/RFC7861,
November 2016, <https://www.rfc-editor.org/info/rfc7861>.
[RFC7862] Haynes, T., "Network File System (NFS) Version 4 Minor
Version 2 Protocol", RFC 7862, DOI 10.17487/RFC7862,
November 2016, <https://www.rfc-editor.org/info/rfc7862>.
[RFC8167] Lever, C., "Bidirectional Remote Procedure Call on RPC-
over-RDMA Transports", RFC 8167, DOI 10.17487/RFC8167,
June 2017, <https://www.rfc-editor.org/info/rfc8167>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
10.2. Informative References
[RFC1094] Nowicki, B., "NFS: Network File System Protocol
specification", RFC 1094, DOI 10.17487/RFC1094, March
1989, <https://www.rfc-editor.org/info/rfc1094>.
[RFC1813] Callaghan, B., Pawlowski, B., and P. Staubach, "NFS
Version 3 Protocol Specification", RFC 1813,
DOI 10.17487/RFC1813, June 1995,
<https://www.rfc-editor.org/info/rfc1813>.
Lever Expires 5 January 2021 [Page 17]
Internet-Draft NFS on RPC-Over-RDMA V2 July 2020
[RFC5040] Recio, R., Metzler, B., Culley, P., Hilland, J., and D.
Garcia, "A Remote Direct Memory Access Protocol
Specification", RFC 5040, DOI 10.17487/RFC5040, October
2007, <https://www.rfc-editor.org/info/rfc5040>.
[RFC5041] Shah, H., Pinkerton, J., Recio, R., and P. Culley, "Direct
Data Placement over Reliable Transports", RFC 5041,
DOI 10.17487/RFC5041, October 2007,
<https://www.rfc-editor.org/info/rfc5041>.
[RFC8178] Noveck, D., "Rules for NFSv4 Extensions and Minor
Versions", RFC 8178, DOI 10.17487/RFC8178, July 2017,
<https://www.rfc-editor.org/info/rfc8178>.
[XNFS] The Open Group, "Protocols for Interworking: XNFS, Version
3W", February 1998.
Acknowledgments
Thanks to Tom Talpey, who contributed the text of Section 6.4.2.
David Noveck contributed the text of Section 6.6 and Section 7. The
author also wishes to thank Bill Baker and Greg Marsden for their
support of this work.
Special thanks go to Transport Area Director Magnus Westerlund, NFSV4
Working Group Chairs Spencer Shepler, Brian Pawlowski, and David
Noveck, and NFSV4 Working Group Secretary Thomas Haynes for their
support.
Author's Address
Charles Lever
Oracle Corporation
United States of America
Email: chuck.lever@oracle.com
Lever Expires 5 January 2021 [Page 18]
Html markup produced by rfcmarkup 1.129d, available from
https://tools.ietf.org/tools/rfcmarkup/