Network World's Storage in the Enterprise Newsletter, 08/08/06

Why current virtual tape libraries may not be meeting your needs
By Mike Karp

Well, another week has passed and likely as not, the total amount of data at your site hasn't shrunk much. Would it surprise you to find that at an identical site across the street, a site housing identical data that is used in identical ways, the amount of data stored had in fact decreased?

How two essentially identical sites with the same data can see differing data growth rates has nothing to do with how the data is used, but everything to do with how the data is managed. Consider the following:

The balancing act between more and more data on the one hand and increasingly aggressive Recovery Time Objectives (RTO) on the other has made the backup and recovery process front line combatants in the push towards increasing IT efficiency. Managers looking for ways to keep ahead of things only found a few technologies that really stand out as having been particularly successful. For many, the best way to cope has proven to be the virtual tape library (VTL).

VTLs have the virtue of looking like tape to all of a shop's existing processes, but - because they are disk-based, (invariably the disks are SATA) - they operate at much faster rates than physical tapes devices. The backed up data resides on the VTL until it can be conveniently offloaded under less-pressured time constraints.

Many admins have gotten used to backing up to VTLs and then staging backups from the VTL to physical tape devices at a later time. Often however, they have found that the data on the VTL, easily accessible because it is kept close to home, also provides the added benefit of rapid and low-cost recoveries that far-surpass their expectations for tape-based recoveries. Many sites are looking a new paradigm: nightly incrementals go to disk; weekly full backups go to tape.

Such rapid recoveries are a good thing of course, but unfortunately, VTLs have the same limitations as other disk-based environments - when you run out of disk, you run out of space to store things. Thus, disk-based recoveries are only available until the VTL runs out of disk space, which has meant that data must be off-loaded at regular - typically weekly - intervals.

Each new generation of tape devices has been able to cram more data onto tape media by improving the media and other basic technologies, and by adding industry-standard data compression techniques. Now a new generation of VTLs is coming onto the scene. It will provide data compression like that offered by tape, but it will also offer a new and much different technology, data de-duplication, that will let admins keep more information on their VTLs than ever before, while at the same time actually storing less data.

Next time, how that will work and what it may mean.

Copyright Network World, Inc., 2006

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