Hi all,
The documentation [0] gives us the following formula for calculating
the number of PG if the cluster is bigger than 50 OSDs:
(OSDs * 100)
Total PGs = ------------
pool size
When we have mixed storage server (HDD disks and SSD disks) and we
have defined different roots in our crush map to map some pools only
to HDD disk and some to SSD disks like described by Sebastien Han [1].
In the above formula what number of OSDs should be use to calculate
the PGs for a pool only on the HDD disks? The total number of OSDs in
a cluster or only the number of OSDs which have an HDD disk as
backend?
Best,
Martin
[0]
http://docs.ceph.com/docs/master/rados/operations/placement-groups/#choosing-the-number-of-placement-groups
[1]
http://www.sebastien-han.fr/blog/2014/08/25/ceph-mix-sata-and-ssd-within-the-same-box/
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