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 <josh.durgin@xxxxxxxxxxx> >> wrote: >>> On 11/09/2012 11:08 AM, Yehuda Sadeh wrote: >>>> >>>> On Fri, Nov 9, 2012 at 11:04 AM, Josh Durgin <josh.durgin@xxxxxxxxxxx> >>>> 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 -- To unsubscribe from this list: send the line "unsubscribe ceph-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
