On kvm documentation you have comands for how move and copy sparse files , perfect , but what is the
command for compress it again in .xz ? for example i made copy the updated and upgrated kvm images in var\lib\libvirt\images to another external usb disk for having backup the whonix , but there are to big -they need 90 GB on disk! * if the compression take to much time , e.g. more than 20 minutes , i thing will be unusable , will better buy a larger disk. Thank you.