[LU-15424] allow 'lfs migrate' for only a single FLR mirror

• Type: Improvement
• Resolution: Unresolved
• Priority: Minor
• Labels: FLR2
• Epic Link: OST rebalance v1
• Assignee: WC Triage
• Reporter: Andreas Dilger

Description

Currently, "lfs migrate" does not work very well for FLR mirrored files. If an FLR mirrored file is migrated, it will replace all of the mirrors with the target layout. It is not currently possible to migrate only a single mirror of a file.

It is not even possible to specify a mirrored layout for the target file ("lfs migrate" apparently doesn't parse the options correctly, and even if this was working it would significant increase write amplification to make multiple copies of a file for the common case of trying to remove objects from a specific OST.

It should be possible for "lfs migrate" to properly migrate only a single FLR mirror of a file by specifying --mirror-id or --comp-id as with "lfs mirror split". Internally, this might be implemented by extending the file with a new FLR mirror using the specified layout and then removing the old mirror, but the user interface should make this transparent.

Issue Links

• is related to: LU-9961 FLR2: Relocating individual objects to a new OST