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cephtest:tipspg

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

cephtest/tipspg.txt · Last modified: 2018/10/11 07:54 by moliver@uclv