Virtual tape library (VTL) technology has been around for many years and was once exclusive to the mainframe domain. Now available from numerous vendors with support for the most popular operating systems (including some Linux), VTLs can emulate many tape devices such as LTO, DLT, 9840, etc.
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But before rushing to the phone to call up your favorite vendor, you must ask yourself a few questions. There are some good reasons for deploying a VTL, but there are also some not-so-good ones.
Some of the good reasons:
- Tape virtualization allows you to take advantage of disk-based backups without actually having to change the way you backup. The virtual drives will look like any other tape drive to most backup software.
- The ability to define multiple virtual libraries allows you to share the VTL between multiple backup servers.
- You can increase the number of tape devices available during backup windows to allow a greater number of concurrent backup streams. You can also use smaller virtual tapes for smaller backups.
- If you have a made a significant investment on a tape subsystem, you can use VTL for onsite backups and physical tapes for vault or archives. You can also replicate remotely between some VTLs, which limits most tape handling to archives only.
Some of the not-so-good reasons:
- You considered dramatically increasing an already high number of physical tape devices for concurrent use on your backup server. Although some VTL appliances allow you to define over 1,000 virtual drives, it doesn't necessarily mean you can -- you must consider other limiting factors in your backup environment. For example, if you are already using twelve LTO 3 drives on your backup server, with each drive capable of up to 80 megabytes per second, you may already be approaching other limitations with your I/O bandwidth or network before adding virtual tape drives. The disk array behind the VTL also has limitations that cannot be ignored.
- An organization that does not have a clearly defined backup data retention policy can actually see some cost increase. Those organizations that keep records indefinitely should review their data retention policies and perform a thorough cost/benefit analysis beforehand -- adding capacity to a VTL can become more costly than simply ordering more tape volumes for a traditional tape library.
Porting VTL technology to open systems was a great advancement in the data protection field. It enables the reduction of media handling, management and physical storage. It also provides an added layer of protection against tape loss. It can replace, provide extra backup resources or become a remote extension to an existing infrastructure. That said, tape virtualization is not a quick fix to a poorly designed backup environment, and it does not address the absence of clearly defined backup policies. Throwing more hardware (even if virtual) at a problem doesn't virtualize the problem itself.
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About the author: Pierre Dorion is a certified business continuity professional for Mainland Information Systems Inc.
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