Thanks for your response. So... if I configured 3 PGs for the pool, would they necessarily each have their primary on a different OSD, thus spreading the load? Or, would it be better to have more PGs to ensure an even distribution?
I was also wondering about the pros and cons performance wise of having a pool size of 3 vs 2. It seems there would be a benefit for reads (1.5 times the bandwidth) but a penalty for writes because the primary has to forward to 2 nodes instead of 1. Does that make sense? -Roland On Thu, May 5, 2016 at 4:13 PM, Michael Shuey <[email protected]> wrote: > 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 > > > -- Roland Mechler Site Reliability Engineer [image: OpenDNS] <http://opendns.com/> Mobile: 604-727-5257 Email: [email protected] *OpenDNS Vancouver* <http://opendns.com/> 675 West Hastings St, Suite 500 Vancouver, BC V6B 1N2 Canada <http://maps.google.com/maps?q=675+West+Hastings+St,+Suite+200%2CVancouver%2C+BC%2C+Canada&hl=en>
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