On Fri, Nov 9, 2012 at 12:26 PM, Josh Durgin <josh.durgin@xxxxxxxxxxx> wrote: > 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 <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. > > > 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. > So maybe instead of having a format version it'll just be a string that specifies either 'rb.' or 'rbd_.'? -- 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
