From: Kai Wagner Date: Fri, 26 Jul 2019 14:55:09 +0000 (+0200) Subject: doc: pg_num should always be a power of two X-Git-Tag: v15.1.0~1996^2~2 X-Git-Url: http://git-server-git.apps.pok.os.sepia.ceph.com/?a=commitdiff_plain;h=3660e17e4b6a681fdca113740ff8b63b17b393d5;p=ceph.git doc: pg_num should always be a power of two Signed-off-by: Kai Wagner --- diff --git a/doc/rados/operations/placement-groups.rst b/doc/rados/operations/placement-groups.rst index 25135d6314b8..cffceda9d475 100644 --- a/doc/rados/operations/placement-groups.rst +++ b/doc/rados/operations/placement-groups.rst @@ -433,9 +433,11 @@ You should then check if the result makes sense with the way you designed your Ceph cluster to maximize `data durability`_, `object distribution`_ and minimize `resource usage`_. -The result should be **rounded up to the nearest power of two.** -Rounding up is optional, but recommended for CRUSH to more evenly balance -the number of objects among placement groups. +The result should always be **rounded up to the nearest power of two.** +A power of two will evenly balance the number of objects among placement groups. +You could set it to a different value but you should be aware that this could result in +an uneven distribution of data across your OSDs. Use of such values shoud be limited to +incrementally stepping from one power of two to another. As an example, for a cluster with 200 OSDs and a pool size of 3 replicas, you would estimate your number of PGs as follows::