But can we change the pg_num of a pool when the pool contains data? If yes, how 
to do this?

-----Original Message-----
From: [email protected] 
[mailto:[email protected]] On Behalf Of Sage Weil
Sent: 2013年2月6日 9:50
To: Mandell Degerness
Cc: [email protected]
Subject: Re: Increase number of pg in running system

On Tue, 5 Feb 2013, Mandell Degerness wrote:
> I would like very much to specify pg_num and pgp_num for the default 
> pools, but they are defaulting to 64 (no OSDs are defined in the 
> config file).  I have tried using the options indicated by Artem, but 
> they didn't seem to have any effect on the data and rbd pools which 
> are created by default.  Is there something I am missing?

Ah, I see.  Specifying this is awkward.  In [mon] or [global],

 osd pg bits = N
 osd pgp bits = N

where N is the the number of bits to shift 1 to the left.  So for 1024 PGs, 
you'd do 10.  (What it's actually doing is MIN(1, num_osds) << N.  
The default N is 6, so you're probaby seeing 64 PGs per pool by default.)

sage


> 
> On Tue, Feb 5, 2013 at 6:40 AM, ArtemGr <[email protected]> wrote:
> > Martin B Nielsen <martin <at> unity3d.com> writes:
> >> Hi,
> >>
> >> Looking at:
> >> http://ceph.com/docs/master/rados/operations/pools/
> >>
> >> It has this description roughly in the middle:
> >>
> >> ---------------
> >> Important
> >> Increasing the number of placement groups in a pool after you 
> >> create the pool is still an experimental feature in Bobtail (v 
> >> 0.56). We recommend defining a reasonable number of placement 
> >> groups and maintaining that number until Ceph?s placement group 
> >> splitting and merging functionality matures.
> >> ---------------
> >>
> >> However, I cannot find any references how to do this?
> >>
> >> I'm asking since we have a test system with 10TB data with only the 
> >> default 8 PG's created.
> >
> > Here's how I do it in ceph.conf:
> >
> > [osd]
> >   ; Increase groups number in order to decrease scrub size
> >   osd pool default pg num = 64
> >   osd pool default pgp num = 64
> >
> >
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