[LU-17822] LMR2a: per-Directory Metadata Replication

• Type: Technical task
• Resolution: Unresolved
• Priority: Minor
• Assignee: WC Triage
• Reporter: Andreas Dilger

Description

Optionally replicate many/all directories in the filesystem.

• Enhance "lfs setdirstripe -N" option to specify replication count, if needed
• Inherit LMR attributes from parent directory by default (with optional "--max-inherit")
• Forbid to set child’s redundancy level less than parent redundancy
  • Otherwise, redundant child may be disconnected and inaccessible if non-redundant parent unavailable

Namespace may still be incomplete, for example a "scratch/" subdirectory tree may be configured without any replicas because it needs performance over availability, but the namespace would at least be consistent and redundant from the root to the parent of "scratch/". Potentially, delayed redundancy could be added to such a directory after it was created and the main workload had finished operating on it.

• Leverage LMR1 tools for conversion between LMR file(s) and non-LMR file(s)
• Enhance LFSCK to handle adding/repairing redundancy, as needed beyond LRM1