qemu-img create -f qcow2 Windows10.qcow2 64G

Convert a raw or VMDK image to QCOW2:

The storage savings and snapshot ability outweigh the minor performance penalty for most workloads – including office apps, web browsing, legacy software, and even light gaming. With proper VirtIO tuning, you likely won’t notice you’re running from a qcow2 file at all.

qemu-img check windows10.qcow2