From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mark Nelson Subject: Re: Questions about journals, performance and disk utilization. Date: Tue, 22 Jan 2013 15:57:02 -0600 Message-ID: <50FF0B2E.6010301@inktank.com> References: <58f5e24e5ac1a7bfff8fc6b90719ec75@skytech.dk> <50FF0197.6020202@inktank.com> <50FF0410.3030308@gmail.com> <50FF098C.8050707@profihost.ag> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from mail-ie0-f179.google.com ([209.85.223.179]:59362 "EHLO mail-ie0-f179.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751490Ab3AVV4w (ORCPT ); Tue, 22 Jan 2013 16:56:52 -0500 Received: by mail-ie0-f179.google.com with SMTP id k14so12419871iea.38 for ; Tue, 22 Jan 2013 13:56:51 -0800 (PST) In-Reply-To: <50FF098C.8050707@profihost.ag> Sender: ceph-devel-owner@vger.kernel.org List-ID: To: Stefan Priebe Cc: Jeff Mitchell , martin , "ceph-devel@vger.kernel.org" On 01/22/2013 03:50 PM, Stefan Priebe wrote: > Hi, > Am 22.01.2013 22:26, schrieb Jeff Mitchell: >> Mark Nelson wrote: >>> It may (or may not) help to use a power-of-2 number of PGs. It's >>> generally a good idea to do this anyway, so if you haven't set up your >>> production cluster yet, you may want to play around with this. Basically >>> just take whatever number you were planning on using and round it up (or >>> down slightly). IE if you were going to use 7,000 PGs, round up to 8192. >> >> As I was asking about earlier on IRC, I'm in a situation where the docs >> did not mention this in the section about calculating PGs so I have a >> non-power-of-2 -- and since there are some production things running on >> that pool I can't currently change it. > > Oh same thing here - did i miss the doc or can someone point me the > location. > > Is there a chance to change the number of PGs for a pool? > > Greets, > Stefan Honestly I don't know if it will actually have a significant effect. ceph_stable_mod will map things optimally when pg_num is a power of 2, but that's only part of how things work. It may not matter very much with high PG counts. Mark