Ceph: PG stuck in "remapped" or "undersized" or "degraded" and no recovery or backfill activity.

Issue

• PG stuck in "remapped" or "undersized" or "degraded" and no recovery or backfill activity (See the Diagnostic section for ceph status example output).
  • Only 1 (or very few PGs) are in this state.
  • From the io: section of ceph status, there is no recovery activity.
  • The system may also be behind is scrubbing as newer versions of Ceph will not schedule scrubbing PGs unless those PGs are active+clean.