Reads will be limited to 1/3 of the total bandwidth. A set of PGs has a "primary" - that's the first one (and only one, if it's up & in) consulted on a read. The other PGs will still exist, but they'll only take writes (and only after the primary PG forwards along data). If you have multiple PGs, reads (and write-mastering duties) will be spread across all 3 servers.
-- Mike Shuey On Thu, May 5, 2016 at 5:36 PM, Roland Mechler <[email protected]> wrote: > Let's say I have a small cluster (3 nodes) with 1 OSD per node. If I create > a pool with size 3, such that each object in the pool will be replicated to > each OSD/node, is there any reason to create the pool with more than 1 PG? > It seems that increasing the number of PGs beyond 1 would not provide any > additional benefit in terms of data balancing or durability, and would have > a cost in terms of resource usage. But when I try this, I get a "pool <pool> > has many more objects per pg than average (too few pgs?)" warning from ceph > health. Is there a cost to having a large number of objects per PG? > > -Roland > > _______________________________________________ > ceph-users mailing list > [email protected] > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com > _______________________________________________ ceph-users mailing list [email protected] http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
