libguestfs tools and virt-sparsify I missed the tool so much that I've been re -google for key word "qcow2 compress", "qcow2 space claim", "libguestfs compress" and etc. for a whole day!!! Here's the manpage: http://libguestfs.org/virt-sparsify.1.html It is much better than the pure qemu-img convert -c -f a.qcow2 -O qcow2 compressed_a.qcow2 command.