On Tue, 19 Jun 2012, Stefan Priebe - Profihost AG wrote:
> Am 19.06.2012 15:01, schrieb Mark Nelson:
> > On 06/19/2012 01:32 AM, Stefan Priebe - Profihost AG wrote:
> > > Am 19.06.2012 06:41, schrieb Alexandre DERUMIER:
> > > > Hi Stephann
> > > > recommandations are 30-50 PGS by osd if I remember.
> > > >
> > > rbd, data and metadata have 2176 PGs with 12 OSD. This is 181,333333333
> > > per OSD?!
> > >
> > > Stefan
> >
> > That's probably fine, it just means that you will have a better
> > pseudo-random distribution of OSD combinations (It does have higher
> > cpu/memory overhead though). Figuring out how many PGs you should have
> > per OSD depends on a lot of factors including how many OSDs you have,
> > how many nodes, CPU, memory, etc. I'm guessing ~180 per OSD won't cause
> > problems. On the other hand, with low OSD counts you could probably have
> > fewer and be fine too.
>
> But this number 2176 of PGs were set while doing mkcephfs - how is it
> calculated?
num_pgs = num_osds << osd_pg_bits
which is configurable via --osd-pg-bits N or ceph.conf (at mkcephfs time).
The default is 6.
sage
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