Mounting NFS Subdirectories Individually Or Just The Parent?

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Hello,

does it in any respect (throughput/performance, cpu load, I/O load, resilience, …) matter, if one mounts subdirectories of an NFS (v3)
export into separate directories or if one just mounts the parent directory?

I.e. like this:

server:/export/base/a -> /mnt/a
server:/export/base/b -> /mnt/b
server:/export/base/c -> /mnt/c
server:/export/base/d -> /mnt/d
server:/export/base/e -> /mnt/e

or simply like this:

server:/export/base -> /mnt

I would guess, that it doesn matter at all, but at $work the standard setup on all cluster nodes is, to mount >20 subdirectories from the NFS
server individually and the justification is, that is more performant and reliable.

Can this be confirmed (or denied)?

I couldn’t find this method of “NFS performance tuning” mentioned anywhere and from a management perspective the sheer amount of mounted filesystems makes the list confusing and harder to troubleshoot.

Any thoughts?

Regards frank

4 thoughts on - Mounting NFS Subdirectories Individually Or Just The Parent?

  • Performance wise, any bottleneck will almost certainly be tied to the disks on the back end, not the nfs process itself.

    There are a couple good reasons for splitting up the mounts:

    1. They can have different export restrictions (e.g., for different
    client hosts, ro vs. rw permissions, user squashing).

    2. /base/[a-e] live on different RAID arrays and might benefit from
    different management cycles; that’d also be a case where multiple
    exports might be a good idea. That said, I’ve never managed an
    exported filesystem consisting of different arrays; we’ve always
    exported at the RAID level or below.

  • There is a slight performance related reason for exporting disk partitions individually, the performance boost is server-side as Paul says. The advantage is that the no_subtree_check can be used without any additional security risk.

    It is probably the case that the /export/base/a is a partition, is exported with no_subtree_check, and therefore there is a small performance boost.

    Preventing server side mount point traversal can also form part of a security mechanism if servers have different security options for different mount points, but in this case mounting server:/export/base wouldn’t give you the same client view of the filesystem tree as mounting each individually if it worked at all.

    Cheers, Sean

  • I’m not sure you can define individual restrictions for subdirectories of exported filesystems? In our case export permissions are set for
    “server:/export/base”.

    Agreed, but this is not the case in our situation.

    frank

  • Exporting them individually also prevents the remote system from accessing /mnt/[!abcde] that you did not intend to make available.

    Jon

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