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**

<code>
ceph osd ls

Sample Output:
 0
 1
 2
</code>
 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**

<code>
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
</code>
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