Network File System Version 4
Internet Engineering Task Force (IETF) T. Haynes
Internet-Draft
Request for Comments: 9737 T. Myklebust
Intended status:
Category: Standards Track Hammerspace
Expires: 25 May
ISSN: 2070-1721 February 2025 21 November 2024
Reporting of Errors via LAYOUTRETURN in NFSv4.2
draft-ietf-nfsv4-layrec-04 via LAYOUTRETURN
Abstract
The Parallel Network File System (pNFS) allows for a file's metadata
(MDS)
and data (DS) to be on different servers. When servers (i.e., the metadata server (MDS)
and the data server (DS)). When the MDS is restarted, the client can
still modify the data file component. During the recovery phase of
startup, the metadata server MDS and the data servers DSs work together to recover state (which files are
open, last modification time, size, etc.). state. If the
client has not encountered errors with the data files, then the state
can be
recovered, avoiding recovered and the resilvering of the data files. files can be
avoided. With any errors, there is no means by which the client can
report errors to the
metadata server. MDS. As such, the metadata server MDS has to assume that a file
needs resilvering. This document presents an extension to
RFC8435 RFC 8435
to allow the client to update the metadata via LAYOUTRETURN and avoid
the resilvering.
Note
This note is to be removed before publishing as an RFC.
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/.
Status of This Memo
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This Internet-Draft will expire on 25 May 2025.
https://www.rfc-editor.org/info/rfc9737.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Definitions . . . . . . . . . . . . . . . . . . . . . . . 3
1.2. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Layout State Recovery . . . . . . . . . . . . . . . . . . . . 3
2.1. When to Resilver . . . . . . . . . . . . . . . . . . . . 4
2.2. Version Mismatch Considerations . . . . . . . . . . . . . 5
3. Security Considerations . . . . . . . . . . . . . . . . . . . 6
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
5. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
5.1. Normative References . . . . . . . . . . . . . . . . . . 6
Appendix A.
Acknowledgments . . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
In the Network File System version4 version 4 (NFSv4) with a Parallel NFS
(pNFS) Flexible File Layout ([RFC8435]) flexible file layout [RFC8435] server, during recovery after a
restart, there is no mechanism for the client to inform the metadata
server (MDS) about an error which that occurred during a WRITE operation
(see Section 18.32 of [RFC8881]) operation to the data servers (DSs) in the
period of the outage.
Using the process detailed in [RFC8178], the revisions in this
document become an extension of NFSv4.2 [RFC7862]. They are built on
top of the external data representation External Data Representation (XDR) [RFC4506] generated
from [RFC7863].
1.1. Definitions
See Section 1.1 of [RFC8435] for a set of definitions.
1.2. Requirements Language
The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL', 'SHALL NOT',
'SHOULD', 'SHOULD NOT', 'RECOMMENDED', 'NOT RECOMMENDED', 'MAY', "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
'OPTIONAL'
"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.
2. Layout State Recovery
When a metadata server an MDS restarts, clients are provided a grace recovery period
where they are allowed to recover any state that they had
established. With open files, the client can send an OPEN operation
(see Section 18.16 of [RFC8881]) operation with a claim type of CLAIM_PREVIOUS
(see Section 9.11 of [RFC8881]). The client uses the
RECLAIM_COMPLETE operation (see Section 18.51 of [RFC8881]) operation to notify
the metadata server MDS that it is done reclaiming state.
The NFSv4 Flexible File Layout Type flexible file layout type allows for the client to mirror
files (see Section 8 of [RFC8435]). With client side client-side mirroring, it
is important for the client to inform the metadata server MDS of any I/O errors
encountered with one of the mirrors. This is the only way for the metadata server
MDS to determine if one or more of the mirrors is are corrupt and then
repair the mirrors via resilvering (see Section 1.1 of [RFC8435]).
The client can use LAYOUTRETURN (see Section 18.44 of [RFC8881]) and
the ff_ioerr4 structure (see Section 9.1.1 of [RFC8435])
structure to inform
the metadata server MDS of I/O errors.
A problem is that arises when the metadata server MDS restarts and the client has errors it
needs to report, it can not report but cannot do so. Section 12.7.4 of [RFC8881]
requires that the client MUST stop using layouts. While the intent
there is that the client MUST stop doing I/O to the storage devices,
it is also true that the layout stateids are no longer valid. The
LAYOUTRETURN needs a layout stateid to proceed proceed, and the client can not cannot
get a layout during grace recovery (see Section 12.7.4 of [RFC8881])
to recover layout state. As such, clients have no choice but to not
recover files with I/O errors. In turn, the metadata server MDS MUST assume that the
mirrors are inconsistent and pick one for resilvering. It is a MUST
because even if the metadata server MDS can determine that the client did modify data
during the outage, it MUST NOT assume those modifications were
consistent.
To fix this issue, the metadata server MDS MUST accept for the
lrf_stateid in LAYOUTRETURN (see Section 18.44.1 of [RFC8881]) the anonymous stateid of all
zeros (see Section 8.2.3 of [RFC8881]) for the lrf_stateid in
LAYOUTRETURN (see Section 18.44.1 of [RFC8881]). The client can use
this anonymous stateid to inform the metadata server MDS of errors encountered. The metadata server
MDS can then accurately resilver the file by picking the mirror(s)
that do does not have any associated errors.
During the grace period, if the client sends a an lrf_stateid in the
LAYOUTRETURN with any value other than the anonymous stateid of all
zeros, then the metadata server MDS MUST now respond with an error of NFS4ERR_GRACE (see
Section of 15.1.9.2 of [RFC8881]). After the grace period, if the
client sends a an lrf_stateid in the LAYOUTRETURN with a value of the
anonymous stateid of all zeros, then the metadata server MDS MUST now respond with an
error of NFS4ERR_NO_GRACE (see Section 15.1.9.3 of [RFC8881]).
Also, when the metadata server MDS builds the reply to the LAYOUTRETURN
when a with an
lrf_stateid with the value of the anonymous stateid of all
zeros zeros, it
MUST NOT bump the seqid of the lorr_stateid.
If the metadata server MDS detects that the layout being returned in the LAYOUTRETURN
does not match the current mirror instances found for the file, then
it MUST ignore the LAYOUTRETURN and resilver the file in question.
The metadata server MDS MUST resilver any files which that are neither explicitly recovered
with a CLAIM_PREVIOUS nor have a reported error via a LAYOUTRETURN.
The client has most likely restarted and lost any state.
2.1. When to Resilver
A write intent occurs when a client opens a file and gets a
LAYOUTIOMODE4_RW from the metadata server. MDS. The metadata server MDS MUST track outstanding write intents
intents, and when it restarts, it MUST track recovery of those write
intents. The method that the metadata server MDS uses to track write intents is
implementation specific, i.e., outside
of the scope of this document.
The decision to resilver a file depends on how the client recovers
the file before the grace period ends. If the client reclaims the
file and reports no errors, the metadata server MDS MUST NOT resilver the file. If
the client reports an error on the file, then the file MUST be
resilvered. If the client does not reclaim or report an error before
the grace period ends, then under the old behavior, the
metadata server MDS MUST
resilver the file.
The resilvering process is broadly to:
1. fence the file (see Section 2.2 of [RFC8435]),
2. record the need to resilver,
3. release the write intent, and
4. once there are no write intents on the file, start the
resilvering process.
The metadata server MDS MUST NOT resilver a file if there are clients with
outstanding write intents. I.e., intents, i.e., multiple clients might have the file
open with write intents. As it the MDS MUST track write intents, it
MUST also track the need to resilver. I.e., resilver, i.e., if the metadata server MDS restarts
during the grace period, it MUST restart the file recovery if it
replays the write intent intent, or else it MUST start the resilvering if it
replays the resilvering intent.
Whether the metadata server MDS prevents all I/O to the file until the resilvering is done or
done, forces all I/O to go through the metadata
server MDS, or allows a proxy server
to update the new data file as it is being reslivered resilvered is all an
implementation choice. The constraint is that the metadata server MDS is responsible
for the reconstruction of the data file and for the consistency of
the mirrors.
If the metadata server MDS does allow the client access to the file during the
resilvering, then the client MUST have the same layout (set of mirror
instances) after the metadata server MDS as before. One way that such a resilvering
can occur is for a proxy server to be inserted into the layout. That
server will be copying a good mirror instance to a new instance. As
it gets I/O via the layout, it will be responsible for updating the
copy it is performing. This requirement is that the proxy server
MUST stay in the layout until the grace period is finished.
2.2. Version Mismatch Considerations
The metadata server MDS has no expectations for the client to use this new
functionality. Therefore, if the client does not use it, the
metadata server MDS
will function normally.
If the client does use the new functionality and the metadata server MDS does not
support it, then the metadata server MDS MUST reply with a NFS4ERR_BAD_STATEID to the
LAYOUTRETURN. If the client detects a NFS4ERR_BAD_STATEID error in
this scenario, it should fall back to the old behavior of not
reporting errors.
3. Security Considerations
There are no new security considerations beyond those in [RFC7862].
4. IANA Considerations
There are
This document has no IANA considerations for this document. actions.
5. References
5.1. Normative References
[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>.
[RFC4506] Eisler, M., Ed., "XDR: External Data Representation
Standard", STD 67, RFC 4506, DOI 10.17487/RFC4506, May
2006, <https://www.rfc-editor.org/info/rfc4506>.
[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>.
[RFC7863] Haynes, T., "Network File System (NFS) Version 4 Minor
Version 2 External Data Representation Standard (XDR)
Description", RFC 7863, DOI 10.17487/RFC7863, November
2016, <https://www.rfc-editor.org/info/rfc7863>.
[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>.
[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>.
[RFC8435] Halevy, B. and T. Haynes, "Parallel NFS (pNFS) Flexible
File Layout", RFC 8435, DOI 10.17487/RFC8435, August 2018,
<https://www.rfc-editor.org/info/rfc8435>.
[RFC8881] Noveck, D., Ed. and C. Lever, "Network File System (NFS)
Version 4 Minor Version 1 Protocol", RFC 8881,
DOI 10.17487/RFC8881, August 2020,
<https://www.rfc-editor.org/info/rfc8881>.
Appendix A.
Acknowledgments
Tigran Mkrtchyan, Jeff Layton, and Rick Macklem provided reviews of
the document.
Authors' Addresses
Thomas Haynes
Hammerspace
Email: loghyr@gmail.com
Trond Myklebust
Hammerspace
Email: trondmy@hammerspace.com