Backup Server divides the database into approximately equal portions, and sends each portion to a different device.
Dumps are made concurrently on all devices, reducing the time required to dump an individual database or transaction log. Because each tape stores only a portion of the database, it is less likely that a new tape will have to be mounted on a particular device.
You can use multiple devices to load a database or transaction log.
Using multiple devices decreases both the time required for the load and the likelihood of having to mount multiple tapes on a particular device.