Re: librbd: error finding header

[Vladimir Bashkirtsev <vladimir@bashkirtsev.com>]

On 13/07/12 01:30, Tommi Virtanen wrote:
> On Wed, Jul 11, 2012 at 9:41 PM, Josh Durgin <josh.durgin@inktank.com> wrote:
>> You're right about the object name - you can get its offset in the
>> image that way. Since rbd is thin-provisioned, however, the highest
>> index object might not be the highest possible object. When you first
>> create an image, only the header object is created.
> You can re-create it with a size that's known to be greater than the
> old size (put in a terabyte extra, or something), and then use a
> partitioning tool to see what the disk layout really is, and resize
> based on that.
Good point. However ceph should not be aware of image internal 
structure. In most installations image would contain partition table 
which obviously may be used to calculate image size but in some cases 
(when whole image is used for something) it may not be. Perhaps good 
point for RBD would be to create first and last object for image when 
RBD header is created. Will waste a bit of space but generally these 
objects will hold partitioning information and just their existence 
would allow to establish boundaries of the image. Does not help with 
snapshots though. But definitely will be helpful for a recovery tool.