A virtual tape library (VTL) is a disk array that mimics tape. To servers, the VTL appears to be a tape library and the data backup software writes to it and manages it as if it were tape. However, because a VTL is disk-based,
Adding a VTL will make it much faster to restore files, folders and even an entire system image from the backup system. A VTL decreases the server backup window because it is so much faster to write to a VTL and the VTL can transfer data to the tape without interfering with the server.
At least half the process of integrating a VTL is easy. "The backup software doesn't need much of a change," says Peter Eicher, director of product marketing for FalconStor Software. VTLs emulate one or more common tape systems, meaning that the VTL is pretty much invisible to the server side.
The other half of the process, connecting the VTL to the physical tape, can be more difficult. This typically requires changing the configuration on the tape system to accept what amounts to a tape image being written to tape. This is easier if the VTL is designed to support the tape system you have, and that's an important consideration in choosing a VTL.
Beyond that, Eicher says there are some other things to consider when integrating a VTL into your system. The most important, he says, is to make sure that the tapes are encrypted when available. "We've had story after story of companies losing tapes or having tapes stolen. If your VTL or backup software supports encryption, use it."
Another thing that will make your life easier is to have the VTL emulate the tape drives you actually use. "That's not absolutely necessary, but it does make the management side easier," he says.
For example, you want the size of your virtual tapes to match your physical tapes. If it is larger, you're going to have to span physical tapes. Many VTLs help this process by creating virtual tape cartridges that can easily work with the physical cartridges on the tape system.
Most VTLs will let you create multiple virtual tape libraries, often with different tape sizes if needed. If you have several servers, you can assign each one to a different virtual library. This helps manage your backups. "In a smaller business, you could have a dedicated [virtual] tape library for every tape backup job," Eicher says. That means no drive sharing on the tapes. "This isn't something that scales infinitely, but it works in small and medium-sized environments," he adds.
Data deduplication is an increasingly popular feature on VTLs. Deduplication can enormously cut down the need for storage space. For example, Hitachi Data Systems claims that its new series of VTLs with built-in deduplication software can compress a petabyte of data down to 50 TB.
However, not all VTLs implement deduplication and not all of them do it in the same way. If you plan to use deduplication, it's important to make sure that your VTL's deduplication features are compatible with your backup software and the rest of your system.
About the author: Rick Cook specializes in writing about issues related to storage and
This was first published in July 2008