On 07/12/2013 02:19 PM, Stefan Priebe - Profihost AG wrote:
Right now I have 4096. 36*100/3 => 1200. As recovery take ages I thought this 
might be the reason.

Are you seeing any craziness on the mons?


Stefan

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Am 12.07.2013 um 17:03 schrieb Mark Nelson <[email protected]>:

On 07/12/2013 09:53 AM, Gandalf Corvotempesta wrote:
2013/7/12 Mark Nelson <[email protected]>:
At large numbers of PGs it may not matter very much, but I don't think it
would hurt either!

Basically this has to do with how ceph_stable_mod works.  At
non-power-of-two values, the bucket counts aren't even, but that's only a
small part of the story and may ultimately only have a small effect on the
distribution unless the PG count is small.

In case of 12 OSDs for each node, and a cluster made with 18 storage
nodes are you suggesting:

(12*18*100) / 3 = 7200 PGs, that rounded to an exponent of 2 means 8192 ?

Well, our official recommendation on the website is PGS = OSDS * 100 / 
replicas.  I think the thought is that with sufficient numbers of OSDs the 
behaviour of ceph_stable_mod shouldn't matter (much).  At some point I'd like 
to do a little more involved of an analysis to see how PG distribution changes, 
but for now I wouldn't really expect a dramatic difference between 7200 and 
8192 PGs.

Mark
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