Thanks Jason, very clear explanation.
However, I found some strange behavior when export-diff on a cloned image, not sure it is a bug on calc_snap_set_diff().
The test is,
Image A is cloned from a parent image. then create snap1 for image A.
The content of export-diff A@snap1 will be changed when update image A.
Only after image A has no overlap with parent, the content of export-diff A@snap1 is stabled, which is almost zero.
I don't think it is a designed behavior. export-diff A@snap1 should always get a stable output no matter image A is cloned or not.
Please correct me if anything wrong.
Thanks,
Zhongyan
On Tue, Nov 22, 2016 at 10:31 PM, Jason Dillaman <jdillama@xxxxxxxxxx> wrote:
On Tue, Nov 22, 2016 at 5:31 AM, Zhongyan Gu <zhongyan.gu@xxxxxxxxx> wrote:
> So if initial snapshot is NOT specified, then:
> rbd export-diff image@snap1 will diff all data to snap1. this cmd equals to
> :
> rbd export image@snap1. Is my understand right or not??
While they will both export all data associated w/ image@snap1, the
"export" command will generate a raw, non-sparse dump of the full
image whereas "export-diff" will export only sections of the image
that contain data. The file generated from "export" can be used with
the "import" command to create a new image, whereas the file generated
from "export-diff" can only be used with "import-diff" against an
existing image.
--
Jason
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