From 3660e17e4b6a681fdca113740ff8b63b17b393d5 Mon Sep 17 00:00:00 2001 From: Kai Wagner Date: Fri, 26 Jul 2019 16:55:09 +0200 Subject: [PATCH] doc: pg_num should always be a power of two Signed-off-by: Kai Wagner --- doc/rados/operations/placement-groups.rst | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) diff --git a/doc/rados/operations/placement-groups.rst b/doc/rados/operations/placement-groups.rst index 25135d6314b..cffceda9d47 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:: -- 2.39.5