Installing on a qcow2 disk image—typically for use in QEMU/KVM , Proxmox , or Virt-Manager —is a popular choice for users needing a lightweight, stable Windows environment with the efficiency of "Copy-on-Write" storage.
Installing Windows 8.1 on a image typically involves using the windows 81 qcow2 install
Virtualization, System Administration, QEMU/KVM Environment: Linux Host, Windows 8.1 Guest Windows 8
to install any remaining drivers (such as the Balloon driver) from the VirtIO ISO. Super User Further Exploration QEMU/KVM Environment: Linux Host
Use virt-manager or add --cdrom virtio-win.iso to your QEMU command line.