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Storage Pipeline: Virtual Tape Libraries

Thankfully, there is a happy medium. VTLs (virtual tape libraries) make a disk array appear to your backup server like a tape library, with no new software or major redesign of your backup processes needed. We invited eight VTL appliance vendors to submit their devices to our New Jersey partner labs. We were able to put seven--EMC Corp.'s Clariion DL300 Disk Library, Maxxan Systems' SVT-100 Virtual Tape System, Network Engines' Virtual Tape Library Appliance, Overland Storage's REO 4000, Quantum Corp.'s DX30, Sepaton's S2100-DS and Ultera Systems' MirageVL Fibre Virtual Tape Controller--to the test. Interestingly, three participating vendors--EMC, Maxxan and Network Engines--use FalconStor's IPStor VirtualTape Library software to power their devices. They've taken different approaches to hardware, however. ADIC declined to send us its Pathlight VX because of a looming major firmware upgrade.

Key to Domestic Harmony

Compared with physical tape, the VTL appliances we tested are blazingly fast, so features and flexibility should be more important in your purchasing decision than raw speed; this is reflected in our scoring. The most obvious difference is in the VTL storage architectures. Systems with internal storage, like the Sepaton S2100-DS and Overland REO 4000, are easy to install but also easy to outgrow. External storage means that a full library doesn't require a forklift upgrade. Other key factors to consider:

  • VTL can emulate multiple libraries. Even though backup software will share a tape library among multiple media servers, they all have to be running the same backup application. With a VTL that can emulate multiple libraries, you can have your Unix systems running Networker and your Windows servers using ArcServe, both backing up to the same RAID array. EMC leads the pack here; its DL300 can emulate 32 libraries.
  • More tape drives mean more simultaneous backup streams and support for more backup media servers for better performance. EMC, Maxxan and Network Engines each support 256 drives. On the other end of the spectrum is Ultera, with one.
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