Dê uma olhada na documentação de referência para os arquivos XML do domínio libvirt, especificamente nesta seção: Hard drives, disquetes, CDROMs .
target
The target element controls the bus / device under which the disk is exposed to the guest OS. The dev attribute indicates the "logical" device name. The actual device name specified is not guaranteed to map to the device name in the guest OS. Treat it as a device ordering hint.
The optional bus attribute specifies the type of disk device to emulate; possible values are driver specific, with typical values being "ide", "scsi", "virtio", "xen", "usb" or "sata". If omitted, the bus type is inferred from the style of the device name (e.g. a device named 'sda' will typically be exported using a SCSI bus).
The optional attribute tray indicates the tray status of the removable disks (i.e. CDROM or Floppy disk), the value can be either "open" or "closed", defaults to "closed". NB, the value of tray could be updated while the domain is running.
Since 0.0.3;
bus
attribute since 0.4.3;tray
attribute since 0.9.11; "usb
" attribute value since after 0.4.4; "sata
" attribute value since 0.9.7