From mboxrd@z Thu Jan 1 00:00:00 1970 From: Josh Durgin Subject: Re: rbd volume upgrades Date: Fri, 09 Nov 2012 12:26:20 -0800 Message-ID: <509D66EC.5070808@inktank.com> References: <509D53BD.6020706@inktank.com> <509D59DC.60706@inktank.com> <509D617E.1050000@inktank.com> <509D62EB.1080508@inktank.com> 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]:53457 "EHLO mail-pb0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751507Ab2KIU0q (ORCPT ); Fri, 9 Nov 2012 15:26:46 -0500 Received: by mail-pb0-f46.google.com with SMTP id rr4so3069161pbb.19 for ; Fri, 09 Nov 2012 12:26:46 -0800 (PST) In-Reply-To: <509D62EB.1080508@inktank.com> Sender: ceph-devel-owner@vger.kernel.org List-ID: To: Alex Elder Cc: Yehuda Sadeh , Gregory Farnum , "ceph-devel@vger.kernel.org" On 11/09/2012 12:09 PM, Alex Elder wrote: > 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. You still need a flag to tell whether there should be an 'rbd_data.' prefix (format 2) or an 'rb.' prefix (format 1) before the object_prefix stored in the header.