Virtual tape library

A virtual tape library (VTL) is a data storage virtualization technology used typically for backup and recovery purposes. A VTL presents a storage component (usually hard disk storage) as tape libraries or tape drives for use with existing backup software.

Virtualizing the disk storage as tape allows integration of VTLs with existing backup software and existing backup and recovery processes and policies. The benefits of such virtualization include storage consolidation and faster data restore processes.

Most current VTL solutions use PATA or SATA disk arrays as the primary storage component due to their relatively low cost. The use of array enclosures increases the scalability of the solution by allowing the addition of more disk drives and enclosures to increase the storage capacity.

The shift to VTL also eliminates streaming problems that often impair efficiency in tape drives as disk technology does not rely on streaming and can write effectively regardless of datatransfer speeds.

By backing up data to disks instead of tapes, VTL often increases performance of both backup and recovery operations. Restore processes are found to be faster than backup regardless of implementations. In some cases, the data stored on the VTL's disk array is exported to other media, such as physical tapes, for disaster recovery purposes (scheme called "disk-to-disk-to-tape", or "D2D2T").

Alternatively, most contemporary backup software products introduce also direct usage of the file system storage (especially network-attached storage, accessed through NFS and CIFS protocols over IP networks) not requiring a tape library emulation at all. They also often offer a disk staging feature: moving the data from disk to a physical tape for a long-term storage.

History

The first VTL solution was an IBM Virtual Tape Server (VTS) introduced in 1997. It was targeted for a mainframe market, where many legacy applications tend to use a lot of very short tape volumes. It used ESCON interface, and acted as a disk cache for 3494 tape library.

Outside of mainframe environment, tape drives and libraries mostly featured SCSI. Likewise, VTLs were developed supporting popular SCSI transport protocols such as SPI (legacy systems), Fibre Channel, and iSCSI.

See also

*Backup
*Disk staging for an alternative approach
*Emulation
*Storage virtualization