On 25/05/18 20:21, David Turner wrote: > If you start your pool with 12 PGs, 4 of them will have double the size > of the other 8. It is 100% based on a power of 2 and has absolutely > nothing to do with the number you start with vs the number you increase > to. If your PG count is not a power of 2 then you will have 2 different > sizes of PGs with some being double the size of the others. Thanks for correctly my wild speculation friendly and with facts. I have spend quite a few hours digging into this I now I understand the issue far better. I did some explanations in other email. > Once upon a time I started a 2 rack cluster with 12,000 PGs. All data > was in 1 pool and I attempted to balance the cluster by making sure that > every OSD in the cluster was within 2 PGs of each other. I have spend some time thinking about the importance of PGs being equal size and realized it depends a lot of the workload, existence of several pools sharing the cluster, etc. In my particular situation (most data under CephFS using quite wide 8+2 erasure code), low activity, immutable data, write once, read many, it seems to be a non issue. I need to think more about it. Having wildly spread of OSD capacity (120 GB - 1TB) seems to be far worse idea. I spend my days reweighting and it is quite difficult to fully utilize the capacity of the cluster. Thanks. -- 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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