On Tue, Oct 02, 2012 at 01:02:06PM -0700, Gregory Farnum wrote:
> Remote and local reservations come out of a different pool?

Yes. This simplifies deadlock prevention.

> I think I know what you're talking about here, but can you provide a
> bit more background on the reservations and stuff?

This is an attempt to limit the amount of recovery operations occurring
at the same time.

Each OSD has a finite number of reservation slots. Reservation requests
are made by PGs to the OSD. A reservation request succeeds immedately if
there are slots available. If none are available, it will succeed after
a reservation is released (freeing a slot).

Before a recovery op may proceed, the primary collects reservations from
itself and all its replicas. If one of the OSDs is busy, the reservation
process will wait until a reservation is available before continuing.
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