Re: Total number PGs using multiple pools

["lidchen@xxxxxxxxxx" <lidchen@xxxxxxxxxx>]

Here are a few values commonly used:

• Less than 5 OSDs set pg_num to 128
• Between 5 and 10 OSDs set pg_num to 512
• Between 10 and 50 OSDs set pg_num to 4096
• If you have more than 50 OSDs, you need to understand the tradeoffs and how to calculate the pg_num value by yourself

But i think 10 OSD is to small for rados cluster.

 

From: Italo Santos

Date: 2015-01-17 05:00

To: ceph-users

Subject:  Total number PGs using multiple pools

Hello,

Into placement groups documentation we have the message bellow:

“When using multiple data pools for storing objects, you need to ensure that you balance the number of placement groups per pool with the number of placement groups per OSD so that you arrive at a reasonable total number of placement groups that provides reasonably low variance per OSD without taxing system resources or making the peering process too slow.”

This means that, if I have a cluster with 10 OSD and 3 pools with size = 3 each pool can have only ~111 PGs?

Ex.: (100 * 10 OSDs) / 3 replicas = 333 PGs / 3 pools = 111 PGS per pool

I don't know if reasoning is right… I’ll glad for any help.

Regards.

Italo Santos

http://italosantos.com.br/

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