Re: rbd volume upgrades

[Josh Durgin <josh.durgin@inktank.com>]

On 11/09/2012 11:08 AM, Yehuda Sadeh wrote:
> On Fri, Nov 9, 2012 at 11:04 AM, Josh Durgin <josh.durgin@inktank.com> 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.

Josh