From mboxrd@z Thu Jan 1 00:00:00 1970 From: Josh Durgin Subject: Re: explicitly specifying pgnum on pool creation Date: Mon, 05 Nov 2012 10:55:31 -0800 Message-ID: <50980BA3.20709@inktank.com> References: Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from mail-pb0-f46.google.com ([209.85.160.46]:37099 "EHLO mail-pb0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932107Ab2KESzu (ORCPT ); Mon, 5 Nov 2012 13:55:50 -0500 Received: by mail-pb0-f46.google.com with SMTP id rr4so4124624pbb.19 for ; Mon, 05 Nov 2012 10:55:50 -0800 (PST) In-Reply-To: Sender: ceph-devel-owner@vger.kernel.org List-ID: To: Sage Weil Cc: ceph-devel@vger.kernel.org On 11/04/2012 03:42 AM, Sage Weil wrote: > The wip-explicit-pgnum changes the 'ceph osd pool create ' > command to require the pg_num value instead of defaulting to 8. This > would make it harder for users to get this wrong. I like this. It'd be great if we could add a pgnum argument to 'rados mkpool' and the corresponding librados pool_create* functions too. > On the other hand, it probably also breaks some scripts for deploying > OpenStack that create volume and image pools. :/ If those scripts are creating pools with 8 pgs, they're going to create problems anyway. I don't mind breaking them as long as it's well documented (i.e. release notes and docs on 'ceph osd pool create' should mention the change). > Ideas? > > The original idea was that the monitor would automagically notice when a > small pgnum pool gets lots of objects and trigger a split. Even if we > don't do that, pretty soon now you'll be able to explicitly increase > pg_num. I still think it might be a good idea to require it up-front, > though. Until split is implemented and well-tested, I think it makes sense to require it up-front. It's easy to relax that requirement later if we want to make it more automatic. > An alternative would be to default to a larger number (say, num_osds << > 2). My concern there is that it makes it easy to create lots of pgs for > pools that may be small, and it's still not large enough to get good > performance for the "create pool, run rados bench" crowd. It would also be easy to create too few pgs, and then add a bunch of osds later. Josh