Question

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

Answer 1

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