Today I played around recovery and backfill of a Ceph cluster (by manually bringing some OSDs down/out), and got one question regards to the current flow:
Does backfill push everything to the backfill target regardless what the backfill target already has? The scenario is like - acting set of the PG is [1, 2, 3], and 3 went down (at which point it already had some data) and stayed down for a sustained period (but not marked out), during which time there were sustained WRITE to the PG. At some point 3 went back up, and it is not sufficient to recovery via PG log, so the PG needed to be backfilled and 3 is the target. Does 1 needs to push everything (last_backfill starts with MIN) to 3? It seems so to me as I don't see some round trip to negotiate what each OSD has and do an incremental push (as recovery does), but it would be nice to get confirm :) Thanks, Guang
