ubuntu@juju-devel3-machine-14:~$ sudo qemu-system-x86_64 -drive format=?
Supported formats: host_floppy null-aio host_device null-co cloop parallels nbd vhdx qcow dmg qcow2 rbd tftp ftp ftps blkdebug sheepdog https quorum http vvfat qed file blkverify vdi vpc raw bochs host_cdrom vmdk