Looking at the docs at [1], I see the following advice:
"When using multiple data pools for storing objects, you need to ensure that you balance the number of placement groups per pool with the number of placement groups per OSD so that you arrive at a reasonable total number of placement groups that provides reasonably low variance per OSD without taxing system resources or making the peering process too slow."
Can someone expound on this a little bit more for me? Does it mean that if I am going to create 3 or 4 pools, all being used heavily, that perhaps I should *not* go with the recommended value of PG = (#OSDs * 100)/replicas? For example, I have 60 OSDs. With two replicas, that gives me 3000 PGs. I have read that there may be some benefit to using a power of two, so I was considering making this 4096. If I do this for 3 or 4 pools, is that too much? That's what I"m really missing -- how to know when my balance is off and I've really set up too many PGs, or too many PGs per OSD.
Somewhat related -- I have one Ceph cluster that is unlikely to ever use CephFS. As such, I don't need the metadata pool at all. Is it safe to delete? That would regain me some PGs, and could lighten the load during the peering process, I suppose.
Thanks,
- Travis
[1] http://ceph.com/docs/master/rados/operations/placement-groups/
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