From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stefan Priebe - Profihost AG Subject: Re: chaning pg_num / pgp_num after adding more osds Date: Tue, 06 Nov 2012 08:32:15 +0100 Message-ID: <5098BCFF.6050004@profihost.ag> References: <5097C9DD.3030600@profihost.ag> <50984F82.3010706@inktank.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from mail.profihost.ag ([85.158.179.208]:39274 "EHLO mail.profihost.ag" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752631Ab2KFHcT (ORCPT ); Tue, 6 Nov 2012 02:32:19 -0500 In-Reply-To: <50984F82.3010706@inktank.com> Sender: ceph-devel-owner@vger.kernel.org List-ID: To: Josh Durgin Cc: "ceph-devel@vger.kernel.org" Am 06.11.2012 00:45, schrieb Josh Durgin: > On 11/05/2012 06:14 AM, Stefan Priebe - Profihost AG wrote: >> Hello list, >> >> Is there a way to change the number of pg_num / pgp_num after adding >> more osds? > > The pg_num/pgp_num settings are only used by mkcephfs at install time. > >> I mean i would like to start with 16 OSDs but i think i'll expand over >> time to up to 100 OSDs. So i think i need to tune pg_num / pgp_num. > > You can specify pg_num when creating a pool: > > ceph osd pool create > > But you don't want to have too many (thousands per osd). Being able > to change the number of pgs in a pool (pg splitting/merging) is in > the works, but in the mean time you can create more pools after you add > a bunch of osds to keep your pg/osd ratio around 100. Thanks Josh for your explanation. I'm not sure if i already understood what pg is at all. First i see that ceph is creating 832 pgs for 12 osds in my case per default. This is 69,3333333 per OSD. You're talking about 100 - is the default calculation broken or hardcoded? When i have one pool with 800 pgs and i add 20 new OSDs how does a new pool help? I mean the old pools will stay with 800 pgs. Thanks again! Greets, Stefan