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    NFS 4.2 Q&A

    Posted by AlexMcDonald

    We received several great questions at our What’s New in NFS 4.2 Webcast. We did not have time to answer them all, so here is a complete Q&A from the live event. If you missed it, it’s now available on demand.

    Q. Are there commercial Linux or windows distributions available which have adopted pNFS?

    A. Yes. RedHat RHEL6.2, Suse SLES 11.3 and Ubuntu 14.10 all support the pNFS capable client. There aren’t any pNFS servers on Linux so far; but commercial systems such as NetApp (file pNFS), EMC (block pNFS), Panasas (object pNFS) and maybe others support pNFS servers. Microsoft Windows has no client or server support for pNFS.

    Q. Are we able to prevent it from going back to NFS v3 if we want to ensure file lock management?

    A. An NFSv4 mount (mount -t nfs4) won’t fall back to an nfs3 mount. See man mount for details.

    Q. Can pNFS metadata servers forward clients to other metadata servers?

    A. No, not currently.

    Q. Can pNfs provide a way similar to synchronous writes? So data’s instantly safe in at least 2 locations?

    A. No; that kind of replication is a feature of the data servers. It’s not covered by the NFSv4.1 or pNFS specification.

    Q. Does hole punching depend on underlying file system in server?

    A. If the underlying server supports it, then hole punching will be supported. The client & server do this silently; a user of the mount isn’t aware that it’s happening.

    Q. How are Ethernet Trunks formed? By the OS or by the NFS client or NFS Server or other?

    A. Currently, they’re not! Although trunking is specified and is optional, there are no servers that support it.

    Q. How do you think vVols could impact NFS and VMware’s use of NFS?

    A. VMware has committed to supporting NFSv4.1 and there is currently support in vSphere 6. vVols adds another opportunity for clients to inform the server with IO hints; it is an area of active development.

    Q. In pNFS, does the callback call to the client must come from the original-called-to metadata server?

    A. Yes, the callback originates from the MDS.

    Q. Is hole punched in block units?

    A. That depends on the server.

    Q. Is there any functionality like SMB continuous availability?

    A. Since it’s a function of the server, and much of the server’s capabilities are unspecified in NFSv4, the answer is – it depends. It’s a question for the vendor of your server.

    Q. NFS has historically not been used in large HPC cluster environments for cluster-wide storage, for performance reasons. Do you see these changes as potentially improving this situation?

    A. Yes. There’s much work being done on the performance side, and the cluster parallelism that pNFS brings will have it outperform NFSv3 once clients employ more of its capabilities.

    Q. Speaking of the Amazon adoption for NFSv4.0. Do you have insight / guess on why Amazon did not select NFSv4.1, which has a lot more performance / scalability advantages over NFSv4.0?

    A. No, none at all.

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