Linux – How to monitor which files are accessed through NFS

Great questions, highlights a bigger point with the documentation IMO. Here is an attempt at a complete answer:

What does "subsequent exports on that line only" mean?

An example's probably easiest here:

/export/stuff -rw 10.0.0.54 10.0.0.55

is equivalent to:

/export/stuff 10.0.0.54(rw) 10.0.0.55(rw)

Is fsid=0 not required anymore?

This depends on your use case. It looks like you are exporting regular disk based filesystems from the rest of your query, in that case you are best to drop fsid=0 (which in nfsv4 changes the behavior to reference the root filesystem of the export).

To change this behaviour remove the no_subtree_check option

rmtab-related stuff

• Is the handling of rmtab a security risk?
  I guess it depends on your use case to answer that, on my network it doesn't present a credible information leak but i can see cases where it could potentially.
• Won't rmtab be full of stale entries?
  Potentially yes, again depending on your deployment scenario / use case.
• Is this why some clients running mount -v erroneously see "nothing was mounted"?
  I've not come across this yet

While storing files in subdirs would be ideal, the right (and expected) behavior is not what you are seeing. Some hints to track down the problem:

• check your source filesystem: if you run your command directly on the data source, does it complete correctly?
• for so many files, your source filesystem should be XFS or ZFS. Avoid EXT4 and BTRFS
• try to toggle client-side caching (FS-cache module)
• does a simple ls -al | wc -l return consistent results?