What are virtual tape libraries?

Nice Answer. This is very clear.

A Virtual Tape Library (VTL) is commonly used for data backup and disaster recovery. It is a virtualization-based data storage technology that pretends to be a tape-based storage device by separating the physical storage, usually in the form of hard disk storage, from the logical storage, which is then presented as tape libraries or tape drives. Why would an IT department want something like this? Sometimes this ‘trick’ is necessary in order to use newer backup storage devices with older, legacy software that’s only able to recognize tape devices. VTLs eliminate the streaming disadvantages associated with tape drives. Specifically, the disk drive in a VTL is able to write and read data non-sequentially and maintain effective data transfer regardless of the transfer speeds. Tape does not have these advantages.

Some software also won’t be able to perform existing backup or recovery processes and polices on a non-tape storage device. Like any other form of virtualization, the main benefits of VTL include the unification of storage management into a single logical storage pool and interface, and it also allows IT departments to include a wide variety of legacy and proprietary storage devices or software into one consolidated pool of storage. The older systems can still be preserved with VTL and virtualization because the separation of logical storage and physical storage allows all of the logical storage of old and new devices to interoperate. Virtualized storage will always facilitate faster data restore processes as well.

PATA (Parallel Advanced Technology Attachment) or SATA (Serial Advanced Technology Attachment) disk arrays are used most often as the primary storage component in VTL solutions. This is because of their relatively low cost. A VTL solution that uses array enclosures will have greater system scalability because it allows more disk drives and enclosures, which increases storage capacity.

The disk storage in a VTL solution is not designed to be removable, so it’s not an optimal solution for archiving. If you still need to use this tape-based system as archival backup, it’s better to just stick with tape storage, which is removable and compatible with your legacy tape-based software. An alternative solution is to just export the data on the VTL’s disk array to other media that is removable. One disadvantage of the disk storage is its constant connection to power sources, making it vulnerable to power surges.

Alternatives to VTL will introduce direct usage of the file system’s storage, especially NAS (Network Attached Storage), which doesn’t require tape library emulation.