This works for recent versions of QEMU. The way to use this is: guestfish <fs> add-drive /dev/null <fs> config -set drive.hd0.file=rbd:pool/volume <fs> run This will probably work for more types (sheepdog, iscsi et al), but with the caveat that the libguestfs layers are bypassed so you'll *always* end up directly accessing the disk in rw mode.