On Tue, Jul 15, 2014 at 9:44 AM, Lakshminarayana Mavunduri
<lakshminarayana.mavund...@sandisk.com> wrote:
> Hi,
>
> Following the below set of steps, we are seeing data loss while reading from
> clones.
>
> 1)Create an image with image format 2 (in this case we have made the size to
> be 1024MB).
> rbd create image1 --size 1024 --image-format 2
> 2)Map the image and write 1024MB worth of data to it.
> 3)Create a snapshot for the image created in step 1)
> rbd snap create image1@snap1
> 4)Create a clone for the snapshot created in step 3)
> rbd clone image1@snap1 clone1
> 5)Create a snapshot for the clone created in step 4)
> rbd snap create clone1@snap2
> 6)Create a clone for the snapshot created in step 5)
> rbd clone clone1@snap2 clone2
> 7)Shrink the size of the clone created in step 4) (in this case we have made
> it to half of its size)
> rbd resize -s 512 --allow-shrink clone1
> 8)Map the clone created in step 6) and try reading 1024MB worth of data.
> 9)Our observation is that, only the first 512MB worth data is intact, the
> rest is not copied over. (In fact, it's only the parent overlap worth data of
> clone1 that is always copied over!)
>
> After the above set of steps, the parent overlap for clone2 would be 1024MB,
> whereas the parent overlap for clone1 would be 512MB. Our understanding is,
> since clone2's parent snapshot is taken before a shrink is performed on
> clone1, any reads worth parent overlap data on clone2 should be serviced from
> it's parent (at least, as long as there are no overwrites done on clone2,
> which is the case here), and we are not finding that to be true in this case.
>
> To augment our theory, if the parent image (a base RBD image, which is not a
> clone) is shrinked, any reads on the clones that are created before the
> shrink, are as expected to our understanding.
>
> Wanted to check if this is indeed a bug or if we are missing anything here.
> The tests are run across ceph version 0.80.
FWIW, I just pushed a fix for this - wip-overlap in ceph-client.git.
Thanks,
Ilya
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