Shrink Qcow2 Disk Files

Linux Guest Preparation

Use the following command to zero out your disk (inside the VM):

# dd if=/dev/zero of=/mytempfile
# rm -f /mytempfile

Shut down the VM.

Create a backup of your existing VM disk file:

# mv image.qcow2 image.qcow2_backup

There are 2 options, one with compression and another without.

# qemu-img convert -O qcow2 image.qcow2_backup image.qcow2

# qemu-img convert -O qcow2 -c image.qcow2_backup image.qcow2

Boot your VM and verify all is working.