Are virtual tape libraries a passing fancy?

With most backup software vendors supporting feature-rich deduplication, the need for VTLs has diminished

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Some backup software can perform deduplication on the client side. While this places more load on the resource being backed up (which may be something you're trying to avoid), it also disperses the load from the backup server and network. In this client-side deduplication scenario, only disk blocks that the backup server hasn't stored for any resource at any point in its active backup history need to be sent across the wire to be stored on the backup host. This may make it possible to centralize backups for WAN-attached servers and get away with a lighter-weight backup server. Since VTLs are not an active part of the backup process -- they just receive and store the backups -- they can't extend deduplication's benefits to this level of the equation.

Nonetheless, in larger environments, the VTL appliance still has an edge in two scenarios.

The first is in performance. While it's true that VTLs are generally constructed from fairly standard server hardware (most I've encountered run some form of heavily customized Linux OS), they are purpose-built to handle the rigors of deduplicating and storing massive amounts of data. While you can certainly do this using general-purpose server hardware and operating systems, at a certain scale there comes a point at which your backup server will start to look like it's desperately trying to be a small SAN. That's generally where the hardware scalability of a VTL may be valuable from a performance perspective.

The second is in the tape emulation functionality that VTLs provide. This emulation may seem like an unnecessary abstraction layer -- after all, its goal is partly to conceal any unusual behavior that backup software wouldn't understand. Now that the backup software most of us use can do the deduplication on its own (sometimes more effectively), is emulating a tape library still desirable? That depends upon what kinds of systems you're backing up. If you have a lot of legacy systems (VMS, AIX, HPUX, etc.) with their own strictly tape-based backup mechanisms, sliding in a VTL can be an excellent way to inject the benefits of disk-to-disk backup and deduplication into architectures that still aren't able to effectively leverage them on their own.

The bottom line is that VTLs are not dead by any means. Large environments that require massive amounts of backup storage and throughput will still be able to leverage benefits unavailable in software-only solutions for some time to come. Small environments, however, will be better suited to general-purpose storage coupled with industry-standard backup software that can dedup on its own.

So if you're re-evaluating your backup strategy and trying to decide whether a VTL is right for you, make sure you pause and consider whether you actually need one. You may be surprised.

This story, "Are virtual tape libraries a passing fancy?," was originally published at Read more of Matt Prigge's Information Overload blog and follow the latest developments in storage at

Copyright © 2010 IDG Communications, Inc.

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