3.5.3. Emulated Storage Devices

The host emulates a range of storage devices that can be presented to virtual machines. Each type of storage device is appropriate for specific use cases. Choice between different types of storage devices allows for maximum flexibility and compatibility with guest operating systems.
virtio-scsi is the recommended paravirtualized storage device for guests using large numbers of disks, or advanced storage features such as TRIM.
virtio-blk is a paravirtualized storage device suitable for exposing image files to guests. virtio-blk can provide the best disk I/O performance for virtual machines, but has fewer features than virtio-scsi.
IDE is recommended for legacy guests that do not support virtio drivers. IDE performance is lower than virtio-scsi or virtio-blk, but it is widely compatible with different systems.
ATAPI CD-ROMs and virtio-scsi CD-ROMs are available for presenting ISO files or the host CD-ROM drive to guests. virtio-scsi CD-ROMs can be used with guests that have the virtio-scsi driver installed. ATAPI CD-ROMs offer wider compatibility but lower performance.
USB mass storage devices and floppy disks
Emulated USB mass storage devices and floppy disks are available when removable media is required. USB mass storage devices are preferable to floppy disks due to their larger capacity.