The format qcow2 support copy-on-write.detail about qcow2 is here. Does libvirt suport clone qcow2 VM Image with copy-on-write. I find none options about:
virt-clone
virt-clone will clone your disk image to the same file format as the original.
If your original disk is an LVM partition then you have to clone to a disk raw format image cause the lvm partition is a raw device
eg:
# virt-clone -d -o winxp -n winxpclone -f winxpclone.img
# qemu-img info winxpclone.img
image: winxpclone.img
file format: raw
virtual size: 5.0G (5368709120 bytes)
disk size: 3.1G
You can convert the cloned disk image to qcow2:
# qemu-img convert -f raw winxpclone.img -O qcow2 winxpclone.qcow2
# qemu-img info !$
qemu-img info winxpclone.qcow2
image: winxpclone.qcow2
file format: qcow2
virtual size: 5.0G (5368709120 bytes)
disk size: 3.1G
cluster_size: 65536
If your VM has a qcow2 file format disk image then virt-clone will clone your disk image to a qcow2 file format
# virt-clone -d -o winxpclone -n winxpcloneclone -f winxpcloneclone.img
# qemu-img info winxpcloneclone.img
image: winxpcloneclone.img
file format: qcow2
virtual size: 5.0G (5368709120 bytes)
disk size: 3.1G
cluster_size: 65536
to resume:
virt-clone will keep the same file format to the cloned disk as the original.
An good solution is to use virt-sparsify
http://libguestfs.org/virt-sparsify.1.html
to reduce the exported disk image size