Are virtual tape libraries a passing fancy?

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

Not long ago VTLs (virtual tape libraries) were central to any enterprise disk-to-disk tape backup strategy. Highly scalable performance and the ability to deduplicate on the fly -- usually without help from backup software -- made them a great wedge to handle the D2D part of the D2D2T equation. But now that all of the major backup software vendors have built in highly effective deduplication, does the VTL appliance still have a home? Or is it our backup strategy that needs a round of deduplication?

To answer that question, it's important to take a step back and really look at what the VTL does. Though the products available in the marketplace vary in terms of features, performance, and scalability, the general idea is that a VTL is a large chunk of high-performance disk with built-in software that fully emulates a physical tape library. They usually allow access via a combination of fiber channel or iSCSI interfaces and also provide some form of block-level deduplication. When using a VTL, the backup software in play doesn't need to know that deduplication is taking place or even really to know that the backup device isn't in fact a real tape library.

[ Also on Get the big picture on backups in W. Curtis Preston's Backup Deep Dive Report. | Looking to revise your storage strategy? See InfoWorld's iGuide on the Enterprise Data Explosion. ]

This emulation makes it possible to build a traditional tape-like backup strategy, while still taking advantage of the flexibility of disk-to-disk backups. What your backup software sees as tape media are actually deduplicated chunks of disk. That means that it's generally possible for the VTL to maintain a truly massive number of backups as compared to your true tape resources, which can't be effectively deduplicated. You can afford to keep months of backups available in your disk-to-disk layer and rarely, if ever, go back to real tapes to restore data you might need. All of this while still being able to manage the resources within your software as if they were real tapes.

So how is operating a VTL any different than using your backup software's own disk-to-disk deduplication functionality pared with a bunch of disks attached to your backup server? The bottom line is that in small-scale deployments, it really isn't. In small environments, you can gain the same benefits that VTLs offer without a separate piece of hardware -- and often do so much more cheaply. In fact, implementing the disk-to-disk backup and deduplication in the software layer can bring some time-saving functionality to the table.

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