On 17/05/18 20:36, David Turner wrote: > By sticking with PG numbers as a base 2 number (1024, 16384, etc) all of > your PGs will be the same size and easier to balance and manage. What > happens when you have a non base 2 number is something like this. Say > you have 4 PGs that are all 2GB in size. If you increase pg(p)_num to > 6, then you will have 2 PGs that are 2GB and 4 PGs that are 1GB as > you've split 2 of the PGs into 4 to get to the 6 total. If you increase > the pg(p)_num to 8, then all 8 PGs will be 1GB. Depending on how you > manage your cluster, that doesn't really matter, but for some methods of > balancing your cluster, that will greatly imbalance things. So, if I understand correctly, ceph tries to do the minimum splits. If you increase PG from 8 to 12, it will split 4 PGs and leave the other 4 PGs alone, creating an imbalance. According to that, would be far more advisable to create the pool with 12 PGs from the very beginning. If I understand correctly, then, the advice of "power of two" is an oversimplification. The real advice would be: you better double your PG when you increase the PG count. That is: 12->24->48->96... Not real need for power of two. Also, a bad split is not important if the pool creates/destroys objects constantly, because new objects will be spread evenly. This could be an approach to rebalance a badly expanded pool: just copy & rename your objects (I am thinking about cephfs). What am I saying makes sense?. How Ceph decide what PG to split?. Per PG object count or by PG byte size?. Thank for your post. It deserves to be a blog!. -- Jesús Cea Avión _/_/ _/_/_/ _/_/_/ jcea@xxxxxxx - http://www.jcea.es/ _/_/ _/_/ _/_/ _/_/ _/_/ Twitter: @jcea _/_/ _/_/ _/_/_/_/_/ jabber / xmpp:jcea@xxxxxxxxxx _/_/ _/_/ _/_/ _/_/ _/_/ "Things are not so easy" _/_/ _/_/ _/_/ _/_/ _/_/ _/_/ "My name is Dump, Core Dump" _/_/_/ _/_/_/ _/_/ _/_/ "El amor es poner tu felicidad en la felicidad de otro" - Leibniz
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