From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alex Elder Subject: Re: rbd volume upgrades Date: Fri, 09 Nov 2012 14:09:15 -0600 Message-ID: <509D62EB.1080508@inktank.com> References: <509D53BD.6020706@inktank.com> <509D59DC.60706@inktank.com> <509D617E.1050000@inktank.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: Received: from mail-ie0-f174.google.com ([209.85.223.174]:51896 "EHLO mail-ie0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755640Ab2KIUJN (ORCPT ); Fri, 9 Nov 2012 15:09:13 -0500 Received: by mail-ie0-f174.google.com with SMTP id k13so6495020iea.19 for ; Fri, 09 Nov 2012 12:09:13 -0800 (PST) In-Reply-To: <509D617E.1050000@inktank.com> Sender: ceph-devel-owner@vger.kernel.org List-ID: To: Josh Durgin Cc: Yehuda Sadeh , Gregory Farnum , "ceph-devel@vger.kernel.org" On 11/09/2012 02:03 PM, Josh Durgin wrote: > On 11/09/2012 11:44 AM, Yehuda Sadeh wrote: >> On Fri, Nov 9, 2012 at 11:30 AM, Josh Durgin >> wrote: >>> On 11/09/2012 11:08 AM, Yehuda Sadeh wrote: >>>> >>>> On Fri, Nov 9, 2012 at 11:04 AM, Josh Durgin >>>> wrote: >>>>> >>>>> On 11/09/2012 11:01 AM, Gregory Farnum wrote: >>>>>> >>>>>> >>>>>> I was asked today if there's a way to upgrade RBD volumes from v1 to >>>>>> v2. I didn't think so, but wanted >>>>>> 1) to make sure I'm right, >>>>>> 2) to ask how hard it would be, >>>>>> 3) to ask if we haven't done it because it didn't occur to us or >>>>>> because it's too hard. >>>>>> -Greg >>>>>> >>>>> >>>>> This was addressed in the original discussions about format 2. >>>>> >>>>> You need to export and then import the volume as format 2. Format 2 >>>>> uses >>>>> different names for objects, so providing an 'upgrade' path would >>>>> still >>>>> require copying all the data around. >>>>> >>>> Couldn't we just set a flag in the header specifying the object naming >>>> version, which would then only require updating the header? >>>> >>>> Yehuda >>> >>> >>> The header was separated from the id object to allow renames to work >>> while the image was in use or with cloning. The whole header format >>> changed and moved to a different object as a result. It would be >>> messy to implement this kind of upgrade, and doesn't provide much >>> benefit when there's an easy way to convert already. If someone really >>> wanted it, it could be implemented, but otherwise I don't think it's >>> worth adding. It would have to be added to the upcoming kernel >>> layering support too. >>> >> >> The assumption is that when you upgrade you don't go back, so the fact >> that the header was separated from the id object doesn't change much. >> An upgrade process would be the same as creating a new v2 image, >> having object names (prefix?) that set as the original object names, >> and with a version field that specifies that these are a v1 names. >> >> The problem that I see with converting v1 to v2 through copy is that >> (besides the cumbersome and potentially very long process) we will end >> up turning sparse data objects into fully written data objects, which >> will affect the data consumption. > > That's a good point about export. It would be good to make export create > sparse files as well, but since it doesn't yet, the in-place upgrade > would be better for space usage. Plus! It looks like you don't even need a flag. I think if you simply recorded the old-format object prefix in the new format header, all would be fine. The format of the object id has not changed between v1 and v2, just the object prefix. -Alex