KVM snapshotting. How to see what’s inside the qcow2 file

kvm-virtualizationqcow2

I use qcow2 file format and create snapshots using a Virt-manager GUI.
I assume I have 100GB disk space and 70% is used by VM at this moment. The qcow2-file size is about 70GB. I create a snapshot. It is stored inside the qcow2-file, we know. After some days the qcow2-file size is rised up to 120GB. OK, we understand, why. I delete this snapshot, but the qcow2-file size does not change!

"qemu-img info" does not show me any snapshots for this qcow2-file! How to see, what's inside this file and how to clean it up?

I've used "qemu-img convert" but I have a feeling inside that it's not the rigth way to decrease the file size.

Best Answer

In order to shrink the image, I'd suggest to use virt-sparsify

export TMPDIR=/var/tmp/
virt-sparsify --check-tmpdir=continue <name>.qcow2 <name>_sparsed.qcow2

Make sure you have enough space in the TMPDIR, otherwise the conversion would crash.

Don't use virt-sparsify on running VM images. You may end up with corrupted image! (see man)

Then you can also use compress option (-c) of the qemu-img convert. However that would probably have some impact on the performance, but probably only during startup and initial load of services.

Related Solutions

Linux – mount qcow2 snapshots

You should apply the snapshot and mount the image like always. It's better to create a snapshot right before applying if you want to turn back to the original disk contents before you do these operations. After you apply the snapshot you just mount the image with qemu-nbd as always:

# modprobe nbd max_part=8
$ qemu-img snapshot -c backup image.qcow2
$ qemu-img snapshot -a old_snapshot image.qcow2
$ qemu-nbd --connect=/dev/nbd0 image.qcow2
# mount /dev/nbd0p1 /mnt

You might want to save snapshot separately and mount it as another disk drive. For this you should use convert comand for qemu-img.

$ qemu-img convert -s old_snapshot image.qcow2 old_snapshot.qcow2
$ qemu-nbd --connect=/dev/nbd0 old_snapshot.qcow2
# mount /dev/nbd0p1 /mnt

See man qemu-img(1) and qemu-nbd(1) for more details.

Free up not used space on a qcow2-image-file on kvm/qemu

virt-sparsify can do all this with less hassle on your part: http://libguestfs.org/virt-sparsify.1.html

Best Answer

Related Solutions

Linux – mount qcow2 snapshots

Free up not used space on a qcow2-image-file on kvm/qemu

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