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I am using qemu-kvm and virt-manager for running virtual machines. There is a snapshot UI in virt-manager to create snapshots. But after creating some snapshots and reverting back to some snapshots, I don't see the vol image file size decreases.

I am using a dynamic sized allocation qcow2 image file. I don't really know how snapshots work here. I don't see virt-manager creates any new images. It's just creating xml files for each snapshot. That's all. For each snapshot, there will be a new xml file in /var/lib/libvirt/qemu/snapshot/my_vm_name/*.xml. There is only one image file for this vm I can find is at /var/lib/libvirt/images/my_vm_name.qcow2.

I am compiling firmwares on this virtual machine. Due to the limited size of my harddrive, I would like to clean everything and free spaces after the compilatioin is completed. But reverting back to a snapshot and deleting snapshots doesn't reduce the size of my_vm_name.qcow2 image file. I just want the image file size to become the old fresh one before the compilation. How can I acheive that? Is that safe just to backup the file itself directly and replace it with the old file when I complete compilation tasks?

Thanks a lot for your help.

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Since nobody replied, what I did is simply copying the image file directly such as cp /var/lib/libvirt/images/my_vm_name.qcow2 backup.qcow2.

Whenever I want to go back to the previous version and file size, I simply delete the existing image and use the old one, something like

# cd /var/lib/libvirt/images/
# rm my_vm_name.qcow2
# cp backup.qcow2 my_vm_name.qcow2

That works so far.

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  • yeah stackexchange is pretty dead on support... Commented Feb 18, 2021 at 5:44

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