Tomado de: https://stackoverflow.com/questions/40771273/ceph-too-many-pgs-per-osd
Before setting PG count you need to know 3 things.
1. Number of OSD
ceph osd ls Sample Output: 0 1 2
Here Total number of osd is three.
2. Number of Pools
ceph osd pool ls or rados lspools
Sample Output:
rbd images vms volumes backups
Here Total number of pool is five.
3. Replication Count
ceph osd dump | grep repli Sample Output: pool 0 'rbd' replicated size 2 min_size 2 crush_ruleset 0 object_hash rjenkins pg_num 64 pgp_num 64 last_change 38 flags hashpspool stripe_width 0 pool 1 'images' replicated size 2 min_size 2 crush_ruleset 1 object_hash rjenkins pg_num 30 pgp_num 30 last_change 40 flags hashpspool stripe_width 0 pool 2 'vms' replicated size 2 min_size 2 crush_ruleset 1 object_hash rjenkins pg_num 30 pgp_num 30 last_change 42 flags hashpspool stripe_width 0 pool 3 'volumes' replicated size 2 min_size 2 crush_ruleset 1 object_hash rjenkins pg_num 30 pgp_num 30 last_change 36 flags hashpspool stripe_width 0 pool 4 'backups' replicated size 2 min_size 2 crush_ruleset 1 object_hash rjenkins pg_num 30 pgp_num 30 last_change 44 flags hashpspool stripe_width 0
You can see each pool has replication count two. Now Let get into calculation
Calculations: Total PGs Calculation: Total PGs = (Total_number_of_OSD * 100) / max_replication_count
This result must be rounded up to the nearest power of 2. Example:
No of OSD: 3 No of Replication Count: 2
Total PGs = (3 * 100) / 2 = 150. Nearest Power of 150 to 2 is 256.
So Maximum Recommended PGs is 256
You can set PG for every Pool
Total PGs per pool Calculation: Total PGs = ((Total_number_of_OSD * 100) / max_replication_count) / pool count
This result must be rounded up to the nearest power of 2. Example:
No of OSD: 3 No of Replication Count: 2 No of pools: 5
Total PGs = ((3 * 100) / 2 ) / 5 = 150 / 5 = 30 . Nearest Power of 30 to 2 is 32.
So Total No of PGs per pool is 32.
Power of 2 Table: 2^0 1 2^1 2 2^2 4 2^3 8 2^4 16 2^5 32 2^6 64 2^7 128 2^8 256 2^9 512 2^10 1024 Useful Commands ceph osd pool create <pool-name> <pg-number> <pgp-number> - To create a new pool
ceph osd pool get <pool-name> <pg_num> - To get number of PG in a pool
ceph osd pool get <pool-name> <pgp_num> - To get number of PGP in a pool
ceph osd pool set <pool-name> <pg_num number> - To increase number of PG in a pool
ceph osd pool set <pool-name> <pgp_num number> - To increase number of PGP in a poo
*usually pg and pgp number is same
