Re: Ceph PG Incomplete = Cluster unusable

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On Wed, 7 Jan 2015 17:07:46 -0800 Craig Lewis wrote:

> On Mon, Dec 29, 2014 at 4:49 PM, Alexandre Oliva <oliva@xxxxxxx> wrote:
> 
> > However, I suspect that temporarily setting min size to a lower number
> > could be enough for the PGs to recover.  If "ceph osd pool <pool> set
> > min_size 1" doesn't get the PGs going, I suppose restarting at least
> > one of the OSDs involved in the recovery, so that they PG undergoes
> > peering again, would get you going again.
> >
> 
> It depends on how incomplete your incomplete PGs are.
> 
> min_size is defined as "Sets the minimum number of replicas required for
> I/O.".  By default, size is 3 and min_size is 2 on recent versions of
> ceph.
> 
> If the number of replicas you have drops below min_size, then Ceph will
> mark the PG as incomplete.  As long as you have one copy of the PG, you
> can recover by lowering the min_size to the number of copies you do
> have, then restoring the original value after recovery is complete.  I
> did this last week when I deleted the wrong PGs as part of a toofull
> experiment.
> 
Which of course begs the question of why not having min_size at 1
permanently, so that in the (hopefully rare) case of loosing 2 OSDs at the
same time your cluster still keeps working (as it should with a size of 3).

Christian
-- 
Christian Balzer        Network/Systems Engineer                
chibi@xxxxxxx   	Global OnLine Japan/Fusion Communications
http://www.gol.com/
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