On Wed, Sep 29, 2021 at 9:34 AM Vladimir Sementsov-Ogievskiy <
vsementsov@virtuozzo.com> wrote:

> Hi all!
>
> Recently we faced the following task:
>
> Customer comes and say: incremental backup images are too fat. Does you
> incremental backup works correct?
>
> What to answer? We should check something. At least check that
> incremental images doesn't store same data twice. And we don't have a
> tool for it. I just wrote a simple python script to compare raw files
> cluster-by-cluster. Then we've mounted the qcow2 images with help of
> qemu-nbd, the resulting /dev/nbd* were compared and we proved that
> incremental backups don't store same data.
>
>
Good idea. I love diagnostic tools!


> But that leads to idea that some kind of that script would be good to
> have at hand.
>
> So, here is a new option for qemu-img compare, that is a lot more
> powerful and effective than original script, and allows to compare and
> calculate statistics, i.e. how many clusters differs, how many
> clusters changed from unallocated to data, and so on.
>
> For examples of output look at the test in patch 04.
>
> Vladimir Sementsov-Ogievskiy (4):
>   qemu-img: implement compare --stat
>   qemu-img: make --block-size optional for compare --stat
>   qemu-img: add --shallow option for qemu-img compare --stat
>   iotests: add qemu-img-compare-stat test
>
>  docs/tools/qemu-img.rst                       |  29 +-
>  qemu-img.c                                    | 275 +++++++++++++++++-
>  qemu-img-cmds.hx                              |   4 +-
>  .../qemu-iotests/tests/qemu-img-compare-stat  |  88 ++++++
>

And new tests! :-)


>  .../tests/qemu-img-compare-stat.out           | 106 +++++++
>  5 files changed, 484 insertions(+), 18 deletions(-)
>  create mode 100755 tests/qemu-iotests/tests/qemu-img-compare-stat
>  create mode 100644 tests/qemu-iotests/tests/qemu-img-compare-stat.out
>
>
>