The current preferred syntax for disk drives uses

  -drive file=/vms/plain.qcow,if=virtio,index=0,boot=on,format=qcow

The new syntax splits this up into a pair of linked args

  -drive file=/vms/plain.qcow,if=none,id=drive-virtio-0,format=qcow2
  -device virtio-blk-pci,drive=drive-virtio-0,id=virtio-0,addr=<PCI SLOT>

SCSI/IDE devices also get a bus property linking them to the
controller

  -device scsi-disk,drive=drive-scsi0-0-0,id=scsi0-0-0,bus=scsi0.0,scsi-id=0
  -device ide-drive,drive=drive-ide0-0-0,id=ide0-0-0,bus=ide0,unit=0