Hi all,
I'm working on algorithm to estimate PG count for set of pools
with minimal input from user. The main target is openstack deployments.
I know about ceph.com/pgcalc/, but would like to write down a rules and
get a python code.
Can you comment following, please?
Input:
* pg_count has no influence on performance except for very small values
* OSD requires a little RAM and CPU to serve each PG
* More PG makes rebalance more smooth
* More PG makes peering longer
* 300 PG per OSD is a good default upper bound
Rules:
* PG per OSD shold be less than 300
* No pool should gets less PG, that some preselected amount (64 for now),
also each pool shold have not less that one PG copy on each OSD
* As cluster may grows - algorithm should takes value near to upper bound
* PG count for a pool should be proportional to data size in the pool.
Algorithm:
* Estimated total amount of PG copies calculated as (OSD * PG_COPY_PER_OSD),
where PG_COPY_PER_OSD == 200 for now
* Each small pool get one PG copy per OSD. Means (OSD / pool_sz) groups
* All the rest PG are devided between rest pools, proportional to their
weights (but no pool should get less PG than minimal count).
By default next weights are used:::
volumes - 16
compute - 8
backups - 4
.rgw - 4
images - 1
* Each PG count is rounded to next power of 2
Thanks
--
Kostiantyn Danilov aka koder.ua
Principal software engineer, Mirantis
skype:koder.ua
http://koder-ua.blogspot.com/
http://mirantis.com
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