Virtual Tape Library (VTL)
A virtual tape library (VTL) is a disk appliance that has special software that makes the device appear as a physical tape drive or tape library to the backup application; the device is accessed through standard tape interfaces. The backup software believes it is writing the backup data to a real tape cartridge when it is, in fact, writing to a specially configured file on the disk appliance. Similarly, the backup software will use the appliance for recovery, accessing the device as if the recovery is coming from tape, when it is actually being transferred from disk spindles on the appliance. At its essence, a VTL is both a disk-based appliance and a tape-like interface.