Re: PG recovery reservation state chart

[Mike Ryan <mike.ryan@inktank.com>]

On Tue, Oct 02, 2012 at 01:31:13PM -0700, Josh Durgin wrote:
> Is the local reservation taken in OSD ID order with the remote
> reservations as well? What's the difference between local and remote
> reservations? Are there different limits on remote and local
> reservations?

They come from separate pools. Each pool has a finite number of
reservations, but if one pool has no more slots the other may still
grant reservations.

> If there's more than one possible replica to backfill from could we try
> to reserve others if the first is busy instead of waiting?

I think you may have your backfill terminology backward. We don't
backfill from a replica, we backfill to a replica.

There will never be more than one replica that needs to be backfilled
to.

> Why would a remote backfill reservation fail if the OSD is full
> (disk space)? Backfill doesn't write to the replica, right? Or by
> full, do
> you mean out of reservations?

If the disk on the OSD is near full we reject backfills. This change I
implemented a few weeks ago and was merged last week.

Backfill does write to the replica.