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I have a VM that was created in raw disk format but learned later that both virsh and qemu-img only supports creating snapshots in qcow2 format.

So I converted my base raw disks to qcow2 and then created snapshots for the disks. The question now is how to apply the snapshot to my base raw disk images?

I tried:

$ qemu-img snapshot -a disk1-snapshot1.qcow2 disk1.img
WARNING: Image format was not specified for 'disk1.img' and probing guessed raw.
         Automatically detecting the format is dangerous for raw images, write operations on block 0 will be restricted.
         Specify the 'raw' format explicitly to remove the restrictions.
WARNING: Image format was not specified for 'disk1.img' and probing guessed raw.
         Automatically detecting the format is dangerous for raw images, write operations on block 0 will be restricted.
         Specify the 'raw' format explicitly to remove the restrictions.
qemu-img: Could not apply snapshot 'disk1-snapshot1.qcow2': -95 (Operation not supported)
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1 Answer 1

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Once you convert the raw disk to qcow2 format, use "qemu-img" for creating a snapshot from base image.

qemu-img create -f qcow2 -b <Base-Image>.qcow2 <Base-Image-Snapshot>.qcow2

The snapshot will have a size of around 200 KB. Further you will need to install new Guest VM which uses snapshot as its disk image.

virt-install --virt-type=kvm --name=<New-Guest-VM> --ram 2048 --vcpus=2 --virt-type=kvm --hvm --network network=default --graphics vnc --disk <Base-Image-Snapshot>.qcow2 --boot=hd --noautoconsole

Now you can start your new Guest VM.

And the snapshot will store only the changes in base image, thus saving a lot of space on your host machine :)

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