On Linux Host: Shut down the VM and run:
Using QEMU directly:
<driver name="qemu" type="qcow2" cache="none" io="native"/> Over time, your Windows 10.qcow2 file grows. Even if you delete files inside Windows, the image file on your Linux host stays large. To reclaim space: Windows 10.qcow2
Inside Windows: Run Defragment and Optimize Drives -> Optimize (This allows the guest to mark free space). On Linux Host: Shut down the VM and