Comment 6 for bug 1774730

I think the qemu-img convert am talking about is used to generate backing file

qemu-img info /openstack/nova/instances/b0dc644d-6f10-4736-806c-946d5649a0be/disk
image: /openstack/nova/instances/b0dc644d-6f10-4736-806c-946d5649a0be/disk
file format: qcow2
virtual size: 25G (26843545600 bytes)
disk size: 308M
cluster_size: 65536
backing file: /openstack/nova/instances/_base/95aa9859731c56d3773d954c1ef0fb45ce8ad799
Format specific information:
    compat: 1.1
    lazy refcounts: false
    refcount bits: 16
    corrupt: false

qemu-img info /openstack/nova/instances/_base/95aa9859731c56d3773d954c1ef0fb45ce8ad799
image: /openstack/nova/instances/_base/95aa9859731c56d3773d954c1ef0fb45ce8ad799
file format: raw
virtual size: 5.0G (5368709120 bytes)
disk size: 3.7G