Monday Sep 02, 2013

IETF 87 NFSv4 Working Group meeting report by Chuck Lever

This is a contributed post from Chuck Lever, who heads up NFS development for the mainline Linux kernel team.

Executive summary:

The 87th meeting of the IETF was held July 28 - August 2 in Berlin, Germany.

I was in Berlin for the week to attend the NFSv4 Working Group meeting and hold informal discussions related to NFS standardization with other attendees. The Internet Engineering Task Force (IETF) produces high quality technical documents that influence the way people design, use and manage the Internet. Essentially, this is the body that regulates the protocols computers use to communicate on the Internet, for the purpose of improving interoperability.

An IETF meeting is held every four months in venues around the world. Sponsorship for each event varies. DENIC, the central registry for domain names under .de, was the primary sponsor for this event. Participation is open to anyone, but a registration fee is required to attend.

NFS version 4 is the IETF standard for file sharing. The charter of the Working Group is to maintain NFS specifications and introduce new NFS features through NFSv4 minor versions. More on the Working Group charter can be found here: http://datatracker.ietf.org/wg/nfsv4/charter/

I attend each NFSv4 Working Group meeting to represent Oracle's interest in various current and new NFS-related features, including pNFS, NFSv4.2, and FedFS. I'm the editor of two of the IETF FedFS protocol specifications, and a co-author of an Internet-Draft that addresses protocol issues affecting NFSv4 migration. Other representatives at this meeting include Microsoft, EMC, NetApp, IBM, Oracle, Tonian, and others. Topics include progress updates on Internet-Drafts on their way to become standards, reports on implementation experience, and requests to start new work or restart old work. See: https://datatracker.ietf.org/meeting/87/materials.html#nfsv4

Meeting agenda, presentation materials, and minutes are available at this location.

Drill down:

Working Group editor Tom Haynes (NetApp) reported on several areas where progress appears to be stalled. In general we face challenges completing our deliverables because the IETF is a volunteer organization, and the tasks at hand are large. The largest item is RFC 3530bis, which is holding up FedFS and NFSv4.2. RFC 3530bis was rejected during IESG review mainly due to the new chapter that attempts to bridge the gap between existing i18n implementations in NFS, and how we'd like i18n to work.

The problem is nobody has implemented i18n for NFSv4, and the IETF has revised i18n since 3530 was ratified. The consensus was to move the offending section to a separate Internet-Draft where the correct language can be hammered out without holding up RFC 3530bis. NFSv4.2 is held up by a lack of enthusiasm for finishing a new revision of RPCSEC GSS. The GSS I-D has languished without an author or editor for many months, and two items in NFSv4.2 depend on its completion: labeled NFS and server-to-server copy. A rough consensus was not achieved, but Tom and Andy Adamson (NetApp) will investigate options, including removing the parts of server copy and labeled NFS that depend on GSSv3, and report back.

Benny Halevy (Tonian) has submitted a fresh draft proposing "Flexible File Layouts" which is a new pNFS layout type that improves upon the existing pNFS file layout defined in RFC 5661. Motivation for a new layout scheme includes: algorithmic data striping to support load balancing, life-cycle management, and other advanced administrative features; support for using legacy NFS servers as pNFS data servers; and direct pNFS support for existing cluster filesystems such as Ceph and GlusterFS.

Chuck Lever (Oracle) described recent progress to address security concerns in the FedFS documents waiting in the RFC Editor queue. He continued by walking through a group of possible future work items, including more modern LDAP security modes, additional administrative operations, and better mechanisms for clients to choose working fileset locations. Does the working group have the energy to consider a new revision of these documents? Or should we continue to focus on making small changes? This was left unresolved.

Sorin Faibish (EMC) discussed the need for a new layout enabling pNFS clients to access Lustre data servers directly. After a lot of discussion, the issue appears to be that the NFS protocol on high performance transports is not performant enough. The proposed solution was to use LNET over RDMA. It was suggested that it would be more interesting to the Working Group if we focused on fixing the performance issues in our RDMA specifications instead.

Marc Eshel (IBM) wanted to restart the age-old conversation on tightening NFS's data cache coherency. The immediate question is whether POSIX semantics are interesting given today's compute workloads and network environment. Implementing POSIX data coherency among multiple networked systems is still a challenge. Consensus that a callback-based solution, where network traffic is proportional to the level of inter-client sharing, was most appropriate. Such a solution (byte-range delegation) was proposed by Trond Myklebust in 2006. It was recommended to start with that work.

Chuck Lever (Oracle) proposed an experimental extension to NFS that enables NFS client and servers to convey end-to-end data integrity metadata. A new I-D has been submitted that describes the protocol changes. No prototype is available yet; the I-D is meant to coordinate discussion of technical details, and enable interoperable prototype implementations.

David Noveck (EMC) elaborated on the need to allow protocol changes outside of the NFS minor version process. He described the limitations of batching unrelated features together and waiting for a full pass through the IETF review process. There was some interest in allowing innovation outside of the minor version process. The Area Directory and Working Group chair felt that there is currently not enough energy behind work already planned for delivery.

Matt Benjamin (Linux Box) is restarting work on a feature proposed several years ago by Mike Eisler that allows directories to be striped across pNFS data servers, just like file data is today. An Internet-Draft is available, and a prototype is underway.

-- Chuck Lever

Thursday Mar 21, 2013

IETF 86 NFSv4 Working Group meeting report by Chuck Lever

This is a contributed post from Chuck Lever, who heads up NFS development for the mainline Linux kernel team.


Executive summary:


On Monday (11th March) I attended the IETF NFSv4 Working Group meeting at IETF 86 in Orlando, Florida.

The Internet Engineering Task Force (IETF) produces high quality technical documents that influence the way people design, use and manage the Internet.  Essentially, this is the body that regulates the protocols computers use to communicate on the Internet, for the purpose of improving interoperability.

An IETF meeting is held every four months in venues around the world.  Sponsorship for each event varies.  This event was sponsored by Comcast and NBCUniversal.  Participation is open to anyone, but a registration fee is required to attend.

NFS version 4 is the IETF standard for file sharing.  The charter of the Working Group is to maintain NFS specifications and introduce new NFS features through NFSv4 minor versions.  More on the Working Group charter can be found here:

http://datatracker.ietf.org/wg/nfsv4/charter/

I attend each NFSv4 Working Group meeting to represent Oracle's interest in various current and new NFS-related features, including pNFS, NFSv4.2, and FedFS.  I'm the editor of two of the IETF FedFS protocol specifications, and a co-author on a draft that discusses experience implementing NFSv4 migration.


Other representatives at this meeting include Microsoft, EMC, NetApp, Oracle, Panasas, and others.  Topics include progress updates on drafts on their way to become standards, reports on implementation experience, and requests to start new work or restart old work.  See:

https://datatracker.ietf.org/meeting/86/materials.html#nfsv4

Meeting slides are available now at this location.  Minutes are coming soon.


Drill down:


Tom Haynes (NetApp) reported on progress with RFC 3530bis, a refreshed specification for NFSv4.0.  This document has passed the Area Director check, and is ready for IESG review.  This document is a top priority because other unfinished documents which cite this document are held up waiting for its completion.

Labeled NFS, a part of the forthcoming NFSv4.2 protocol, has a Linux prototype that was demonstrated at Connectathon last month.

The RPCSEC_GSSv3 standard has not made progress, but an editor (Dros Adamson) was assigned during IETF 85.  This document is blocking progress on NFSv4.2.

The NFSv4.2 draft is in WG last call, which ends today (Monday, March 11).  No new issues were raised, so the Working Group chair will move this forward.

Tom Haynes presented a brief set of slides on how NFSv3 client should interpret the presence of AUTH_NONE in the list of security flavors a server supports.  There was never a formal standard describing this, and now we need an interoperability document.  As we explore this issue we may discover some real problems.  A fresh draft was requested.

Dave Noveck (EMC) discussed progress on the draft co-authored with Bill Baker, Piyush Shivam, and myself on NFSv4 migration issues.  As part of the discussion, we visited the issue of how to prevent client progress when a server freezes open and lock state before a migration.  Adding a new error code was mentioned, but that is against the minor version rules and would cause interoperability problems with clients that don't recognize the new error code.  Otherwise we have the procedural issues taken care of to advance this document to become an informational RFC.

A draft covering NFSv4.1 migration issues would probably not be needed, as the changes are small and could be covered in an RFC 5661bis, when it is opened.  There doesn't seem to be urgency here.

Chuck Lever (Oracle) described implementation experience with the recommendations of Dave's migration draft.  The experience arises from the Linux Uniform Client String changes Chuck has done, and a number of items discovered by the Solaris NFS team.

Chuck Lever reported on progress with the FedFS draft standards.  Short story: They are in the RFC Editor queue awaiting completion of RFC 3530bis.

Trond Myklebust (NetApp) presented an issue with NFSv4.1 session slot table management that he also has reported at Connectathon.  It was agreed that an errata to RFC 5661 would be produced that describes how implementations will add missing behavior.  No on-the-wire protocol changes.

Matt Benjamin (The Linux Box) requested a revisit of a 2008 proposal by Mike Eisler to stripe POSIX directories across multiple data servers.  An algorithm would generate an offset into a table of device IDs, which would indicate on which data server to find a directory entry.  Matt claimed there would be changes to the proposal to deal with Ceph and CohortFS.  Chair requested a draft, Matt to deliver soon.

Chuck Lever asked if we still need an NFS-specific mechanism for provisioning NFSv4 ID domain names.  The feeling is that this domain name is determined by the system's authentication service, not by NFS, so NFS should not have its own way to set this.  Consensus that there is some work to do here, and it should be done under umbrella of the ongoing multi-domain work.

Spencer Shepler (Microsoft) closed the meeting with a house-keeping item.  There is some desire to reduce travel by moving more work to the mailing list.  The plan is to ask about agenda items for a meeting before requesting a meeting slot at the next IETF.

Several folks wanted to discuss Bill Baker's micro-versioning proposal.  Dave Noveck stated the problem this way: NFSv4.1 is a heavyweight minor version with a bunch of features, so fixes for 4.0 aren't possible with our spiffy minor versioning scheme.  Spencer felt we should visit this only when we encounter a problem we must address with major protocol changes.  The room was divided; some felt waiting was best so that a problem statement can be formulated; others were concerned that it was almost certain we would need to alter the NFSv4.0 XDR at some point, and we should start working this out now.

In the near term, protocol issues should come to the mailing list sooner rather than later so we can work them out together.

-- Chuck Lever

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The Oracle mainline Linux kernel team works as part of the Linux kernel community to develop new features and maintain existing code.


Our team is globally distributed and includes leading core kernel developers and industry veterans.


This blog is maintained by James Morris <james.l.morris@oracle.com>

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