qemu-img compression: how to preserve snapshots?

atelszewski · 09-16-2017, 08:45 PM

Hi,

QEMU: 2.10.0.
libvirt: 3.4.0.

I have an image like that:

Code:

$ qemu-img info buildbot.qcow2 
image: buildbot.qcow2
file format: qcow2
virtual size: 128G (137438953472 bytes)
disk size: 25G
cluster_size: 65536
Snapshot list:
ID        TAG                 VM SIZE                DATE       VM CLOCK
2         upgraded                  0 2017-09-17 00:53:38   00:00:00.000
3         fresh install             0 2017-09-17 00:58:10   00:00:00.000
Format specific information:
    compat: 1.1
    lazy refcounts: false
    refcount bits: 16
    corrupt: false

Then I compress it like that:

Code:

qemu-img convert -p -c -f qcow2 -O qcow2 -- buildbot.qcow2 buildbot.new.qcow2

And the resulting image looks like that:

Code:

image: buildbot.new.qcow2
file format: qcow2
virtual size: 128G (137438953472 bytes)
disk size: 6.5G
cluster_size: 65536
Format specific information:
    compat: 1.1
    lazy refcounts: false
    refcount bits: 16
    corrupt: false

that is, the snapshots information is lost.

Is it possible to compress the image and preserve snapshots information?

Better yet, is it possible to compress with virsh/libvirt?

--
Best regards,
Andrzej Telszewski

atelszewski · 12-18-2017, 09:51 AM

Hi,

To blindly answer my own question, what I wanted might not be possible.
Or at least I haven't found anything that could help.

I reverted back to the old way of managing my disk images.
I.e. I use backing file and I discard or commit the changes when I see fit.

This solves also another problem, that is, the hardware configuration is not saved by libvirt, as it is when using snapshots.
This might or might not be a good thing, but in my use case, it is the good one ;-)

--
Best regards,
Andrzej Telszewski

jefro · 12-18-2017, 02:15 PM

Thanks for the update and solution. Maybe someone will add to this if they have some more information.