"Learning Ceph" book gives us the following formula:
PGs = OSDs × 100 / (replicas × pools)
Saying, you have 10 OSDs and 5 pools with replica 2, you get:
PGs = 10 × 100 / (2 × 5) = 100 PGs (per pool)
It is also advised to round PGs count up to nearest power of 2. In this
case, to 128.
In typical small cluster, I believe you should never user less than 32
PGs per pool and rarely more than 128. One may start from 64 and adjust
this value as needed to higher one (as you cannot decrease PGs, only
increase).
13.11.2015 08:12, wah peng написав:
Hello,
what's the disadvantage if setup PG_Number too large or too small
against OSD number?
Thanks.
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