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Virtual tape libraries: Buyers beware

Missing tapes, or tapes that don't fit anywhere, are just some of the unwanted surprises users can face when recovering data from a virtual tape library.

Virtual tape library (VTL) technology, or front-end software that transforms disk into virtual tape to improve backup and recovery times, has great potential -- but there are some nasty traps to watch out for.

The biggest one, according to a recent study by Strategic Research Corp., centers on recovery, which always takes place through the backup application.

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The safest method is to allow the media server (the one that runs with the backup application) to handle the movement of data from disk to tape. However, only a few virtual tape systems on the market adhere strictly to this approach, according to Michael Peterson, president of Strategic Research Corp. All others have a "backdoor" trap allowing the virtual tape system to have direct control of data migration to tape, bypassing the media server.

"This is a huge problem because if the media server doesn't know where the data is, then it can't recover it," Peterson said. The safest approach is not to create tapes, or move data directly from the virtual tape appliance to tape using the VTL.

Curtis Preston, VP of service deployment at Glasshouse Technologies Inc., said users should be aware that this method has extra manageability issues but that it "in no way" means a company's data is at risk. "It's just an extra step you will have to make when a copy fails."

Who are the culprits?

Companies that promote the use of a secondary media manager inside the VTL include: FalconStor Software Inc.'s VTL, EMC Corp.'s Clariion Disk Library, Alacritus Software Inc.'s Securitus, Maxxan Systems Inc.'s SVT100 and SVT200, and Neartek Inc. Those that avoid this problem, meaning that they only allow tape management through the backup application and its media server, include: Diligent Technologies Corp., Quantum Corp. and Sepaton Inc.

Both FalconStor and ADIC with its PathLight VX, say that they avoid the problems mentioned by Peterson in their systems with a bar code that the backup software can track between both the virtual and the physical tape. So if a tape is taken off site, the backup software is still aware of it.

The Tape Technology Council advises users to create automated media management throughout the life cycle of the tape. A solution must provide the ability to manage each volume from the moment it is first written to, until the time it is retired. The Council suggests any backup system also requires tracking the tapes location, whether in the library or offsite, and reporting on its usage, current location and other critical metrics.

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