[LU-13076] DNE3: lfs migrate -m should allow -1 as the target index

• Type: Improvement
• Resolution: Fixed
• Priority: Minor
• Fix Version/s: Lustre 2.15.0
• Labels: dne3
• Assignee: Lai Siyao
• Reporter: Andreas Dilger

Description

When migrating directory trees to new MDTs for space balancing, it would be very convenient to allow specifying "lfs migrate -m -1" to have "lfs" pick the MDT with the most free inodes as the target. This is similar to "lfs setdirstripe -i -1" functionality, but for migration. If multiple directories are specified on the command line, it probably makes sense to refresh the statfs information after each directory tree is migrated, in case there is a new MDT that has more free space. This will greatly simplify directory migration on an existing filesystem without the user having to specify the details.

If this is already implemented (it didn't look like parse_targets() would handle 1 as an argument), then the lfs-migrate.1 man page needs to be updated with this information under the description of -mdt-index.

I suspect this would be relatively easily implemented in Lustre 2.12, because the mechanism to select the best MDT is already present in lfs.

Issue Links

• is related to: LU-14975 DNE3: directory migration in non-recursive mode
• is related to: LU-14210 DNE3: "lfs migrate -m" should allow-non-recursive migration