How to reduce the size of KVM QCOW2 images that grow out of hand

Photo by frank mckenna on Unsplash

This is a very short and practical article useful to anyone who uses KVM in production and somehow needs to reduce the space used by a QCOW2 disk image. It is not enough to just free up space from the VM itself. Once a QCOW2 grows in size it never goes back down, on its own accord.

To do this quickly and safely I recommend the following steps:

1. Free up any space in the disk from within the VM
2. Shutdown the VM
3. Backup the disk image that you want to reduce(Optional, if have a lot of faith in Unix commands that you never heard about before )
4. from the directory where your image is stored call:
   virt-sparsify — in-place defenders-disk01.qcow2
5. Once the command completes successfully, restart the VM
6. Verify that the disk space usage went down using df -kh. Should work.

Resources

virt-sparsify

Resizing KVM qcow2 images