PowerScale: NFSv4 mounts fail while NFSv3 mounts of the same path succeed

Attempt to mount an export returns a Permission-Denied error when using NFSv4 but succeeds when using NFSv3 or when using an NFS Alias.

Client Example

Here is an example of a client being denied access using NFSv4, while being allowed access using NFSv3, or using an NFS Alias.

Mounting the full path with NFSv4 shows access denied:

client@client-1:~ $ sudo mount -o vers=4 x.x.x.x:/ifs/narrow/wide /mnt/isi mount.nfs: access denied by server while mounting x.x.x.x:/ifs/narrow/wide

Mounting with NFSv3 suceeds:

client@client-1:~ $ sudo mount -o vers=3 x.x.x.x:/ifs/narrow/wide /mnt/isi
client@client-1:~ $ ls /mnt/isi wide.file 
client@client-1:~ $ sudo umount /mnt/isi 

Mounting as NFSv4 with an Alias succeeds:
client@client-1:~ $ sudo mount -o vers=4 x.x.x.x:/wide /mnt/isi 
client@client-1:~ $ ls /mnt/isi wide.file 

And here is an example of a common permission set that would cause this issue as viewed from the cluster.

cluster-1# ls -l /ifs | grep narrow
drwx------ 3 root wheel 51 Jul 19 16:49 narrow

cluster-1# ls -l /ifs/narrow | grep wide
drwxrwxrwx 2 root wheel 27 Jul 19 16:37 wide

Notice that on narrow everyone is missing execute permissions on /ifs/narrow

This issue stems from differences in NFSv3 vs NFSv4 mount handling and occurs with all Linux NFS servers when mounting using NFSv4.

Unlike NFSv3, NFSv4 mounts walk the directory tree (RFC7530 §7), performing LOOKUP, and READDIR for each segment. For example, mounting /ifs/narrow/wide requires execute permissions on /ifs and /ifs/narrow.

There are two possible solutions:

Allowing Everyone the execute permission.

The most secure fix is to grant the execute (x) permission on all directories in the path. This allows traversal, not listing or modification.

NFS Alias

If execute permissions are not desired, creating an NFS alias works around the requirement for execute on each directory in the path. See NFS Alias section in Dell PowerScale: OneFS NFS Design Considerations and Best Practices.