On Mon, Jul 1, 2013 at 9:15 AM, Alex Bligh <alex@xxxxxxxxxxx> wrote: > > On 1 Jul 2013, at 17:02, Gregory Farnum wrote: > >> It looks like probably your PG counts are too low for the number of >> OSDs you have. >> http://ceph.com/docs/master/rados/operations/placement-groups/ > > The docs you referred Pierre to say: > > "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." > > but they do not tell you how to increase that number (whether it's experimental or not) after a pool has been created. Oh, that's out of date! PG splitting is supported in Cuttlefish: "ceph osd pool set <foo> pg_num <number>" http://ceph.com/docs/master/rados/operations/control/#osd-subsystem > Also, they say the default number of PGs is 8, but "When you create a pool, set the number of placement groups to a reasonable value (e.g., 100)." If so, perhaps a different default should be used! Unfortunately the system would require a lot of smarts in order to do this effectively — for some pools 8 might be appropriate, for others it needs much more. Our usual rule of thumb (referenced on that first page) is 100 PGs/OSD. We plan to build automatic PG split/merge — based on the amount of data in the pool, its distribution, etc — into the system at some future point, but we aren't there yet (for one thing, we don't have merging). -Greg Software Engineer #42 @ http://inktank.com | http://ceph.com _______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
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