What is a Virtual Tape Library?

R. Kayne

A virtual tape library (VTL) combines tape backup emulation software with hard disk architecture to provide a superior archival backup solution. It is faster, more flexible, more robust, and more cost-effective than tape backup. Since VTL uses disk-to-disk (D2D) backup, it is sometimes referred to as VTL D2D.

A virtual library may refer to a space where books can be read, such as computers and the Internet.
A virtual library may refer to a space where books can be read, such as computers and the Internet.

While tape drives were the method of choice for archival backup throughout the 1990s, the medium of magnetic tape has its share of inherent drawbacks. Searching for cartridges, accessing the information, and copying files can take several minutes at best, providing the backup drive and cartridge perform as expected. At the beginning of the new millennium, hard disks became affordable enough to make them a feasible and welcome alternative to tape backup. Enter the virtual tape library, a backup solution that offers all the convenience of tape methodology with the speed and reliability of hard disks. Access to files using a VTL is instant, and though hard disks have moving parts, they are far more reliable than magnetic tape.

A virtual tape library is also convenient in other ways. Using disk arrays, one can potentially store up to a terabyte of data or more in a few large-capacity hard disks that take up little more room than a laptop. Using RAID arrays that read the disks as a single large drive, the data is located in "one place" rather than spread among cartridges. Workstations configured with the proper credentials can access the VTL without expending additional employee resources to handle the backup unit and administer backup or restore services.

A virtual tape library uses tape emulation software for backup strategies. This makes it compatible for implementing into an existing tape backup structure. A virtual tape library can also be part of a redundant backup strategy that involves hard disk backup as the primary source, and tape backup as a secondary library. Cartridges can be stored in a safe place off the premises for maximum security. In case of fire or theft, the tape library will still be available to rebuild the system. Using this strategy, cartridges are also made available for transport to other offices or locations in which a network may not exist.

If your network does not currently use a tape library, you may be interested in using true D2D rather than a virtual tape library, or VTL D2D. True D2D is not restricted to tape-like emulation and can use external redundant disks as a mobile secondary backup archive. Software for D2D is available for RAID and non-RAID disk arrays.

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Discussion Comments


I think it is just a software interface so that old backup software won't choke on new system - in the name of backward compatibility. Other than that, if you don't have tape backup system now, then D2D is your option. Duc K.


After reading through this article and the one on tape backups, it's just not clear to me exactly what "convenience" of tape systems is emulated in a VTL. Is it the sequential storage? That seems to be a big, fat drawback. Perhaps it's the incremental nature of the backups? That can be done on a hard drive without emulating tapes. In fact, I'm not really all that sure exactly what about tapes a VTL is emulating. How is it different than just backing up on a hard drive?

Terence P Ward

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