Yes, it's expected. The crush map contains the inputs to the CRUSH hashing algorithm. Every change made to the crush map causes the hashing algorithm to behave slightly differently. It is consistent though. If you removed the new bucket, it would go back to the way it was before you made the change.
The Ceph team is working to reduce this, but it's unlikely to go away completely.
On Sun, Apr 5, 2015 at 11:45 AM, Andrey Korolyov <andrey@xxxxxxx> wrote:
Hello,
after reaching certain ceiling of host/PG ratio, moving empty bucket
in causes a small rebalance:
ceph osd crush add-bucket 10.10.2.13
ceph osd crush move 10.10.2.13 root=default rack=unknownrack
I have two pools, one is very large and it is keeping up with proper
amount of pg/osd but another one contains in fact lesser amount of PGs
than the number of active OSDs and after insertion of empty bucket in
it goes to a rebalance, though that the actual placement map is not
changed. Keeping in mind that this case is very far from being
offensive to any kind of a sane production configuration, is this an
expected behavior?
Thanks!
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