One Tuesday, she ran into a problem. She needed to test a new strain of ransomware, but she was running out of disk space on her server. Her Windows 7 VM was configured as a "raw" disk image, meaning it took up the full 50GB of allocated space, even though the OS only occupied 12GB.

When creating the image, use a larger cluster size for sequential workloads:

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Once installed, Windows 7 might feel sluggish on virtual hardware. Apply these tweaks:

To see how much space a QCOW2 image is actually using vs. its virtual size: qemu-img info windows7.qcow2 Use code with caution. Converting Raw to QCOW2

Windows 7 retains driver references from the old hypervisor. Boot the new Qcow2 image via QEMU, press F8 before Windows loads, select "Safe Mode." Once in Safe Mode, run sysprep with the "Generalize" option (from C:\Windows\System32\sysprep\sysprep.exe ). This strips old HAL and storage drivers, forcing Windows 7 to rediscover the VirtIO environment.