[lustre-discuss] Mounting subdirectories of the same lustre file system separately on a single host

[Nathan Dauchy]

Kurt,

Your plan should work fine and subdir mounts is certainly something which has been used with Lustre already.  A couple caveats and notes:

  *
not all clients need the same mounts, which is important because you want to write data to that 'ro' dir somehow. 😉
  *
there were some bugs with lfs, PCC, and other tools not working quite right on subdir mounts.  I think all the ones that we were hitting have been addressed, but you may want to take a look at LU-8585: "All Lustre test suites should pass with subdirectory mount"
  *
some operations, such as changing filesystem default striping, still require a mount of the root dir AFAIK.  So have a plan of where and how you will access that when needed.

Regards,
Nathan

________________________________
From: lustre-discuss <lustre-discuss-bounces at lists.lustre.org> on behalf of Kurt Strosahl via lustre-discuss <lustre-discuss at lists.lustre.org>
Sent: Wednesday, August 28, 2024 2:28 PM
To: lustre-discuss at lists.lustre.org <lustre-discuss at lists.lustre.org>
Subject: [lustre-discuss] Mounting subdirectories of the same lustre file system separately on a single host

Good Afternoon,

   We are exploring ways to have a directory tree within one of our lustre file systems set to be read only, while the rest of the tree remains in a read/write state.  Since the directory is at the base of the lustre file system one thought is to mount that branch with the ro flag, and the other branchs would be mounted as rw.

Are there any complications or issues that come with having branches of the same lustre file system mounted on the same system at the same time?

In short we are looking to go from:
/lustre mounted on /lustre (rw)

to
/lustre/dir1 mounted on /dir1 (ro)
/lustre/dir2 mounted on /dir2 (rw)
/lustre/dir3 mounted on /dir3 (rw)

w/r,

Kurt J. Strosahl (he/him)
System Administrator: Lustre, HPC
Scientific Computing Group, Thomas Jefferson National Accelerator Facility
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