This is a libvirt question, so asking it on the qemu-block might not get you an answer that quick, ... or ever if I didn't notice your other question also addressed incorrectly. [adding libvirt-users(a)redhat.com to cc] On Tue, Sep 01, 2020 at 10:57:34 -0400, Yoonho Park wrote: Could you please elaborate on the exact steps? specifically the arguments for qemu-img create. My feeling is that you didn't specify the backing image format (-F) when creating the overlay, but it's hard to tell from this very sparse question. virsh attach-disk is a syntax-sugar wrapper which generates the XML document which is in fact used to attach disk. You can use virsh attach-disk --print-xml to see what would be used. using virsh attach-device allows you to pass in a whole <devices> subelement such as <disk> with any configuration you are able to specify when defining the XML. The virsh attach-disk is limited to just "basic" config options.