Automating Tape Backups

The Need for Speed

Before you buy a tape autoloader, consider the size of your backup window. This will help determine your optimal tape-drive speed. The more capacity you have, the greater your speed requirements will be. The Quantum DLT600 drive, for instance, can handle up to 36 MB per second native (noncompressed), compared with Exabyte's VXA-2 drive, which can handle only 6 MBps native, or Sony's AIT1 drive, which handles a mere 4 MBps native.

In the tape industry, compression is applied to both the transfer rate and the total capacity of a tape drive. Because anything listed as "native" is considered to be noncompressed and can represent a worst-case scenario, tape drive manufacturers don't highlight those numbers in their product literature. So unless a great quantity of your backup data is already compressed, expect an average data-compression ratio of 2:1. And though some companies claim a faster compression algorithm--Sony, for instance, lists its compression ratio at 2.6:1--we strongly urge you to use the 2:1 ratio in your estimate.

Give Me Space

Slot count multiplied by the capacity of an individual tape is the equation used to determine the capacity of the entire automation setup. Some tape autoloaders offer more expandability, letting you "stack" additional capacity and tape drives. In some cases, what you stack may be just cartridge slots, but in many instances you will stack another entire tape autoloader using a pass-through mechanism.

If you expect to buy extra capacity to accommodate your projected data growth, we encourage you to question the manufacturer on the reliability of its pass-through mechanisms, which can often pose problems.

Ask about jam and failure rates. The more drives you stack, the faster your backups. But more speed doesn't necessarily mean more capacity. Extra drives let you shorten the backup window, but will not significantly increase the capacity.

Here, again, the five-year model can serve you well. If you aren't sure the unit you're considering can be complemented with a reliable pass-through mechanism, get enough slots in the original base chassis to accommodate your projected five-year data growth. But be certain any backup software you use is certified to work with the autoloader you purchase.Buying an autoloader isn't like buying a toaster. The physical environment in which you set up the equipment is just as important as the product's capacity and speed.

Most autoloading products take up no more than 20u. Unless the space at the installation site is tiny, most autoloaders, even some of the higher capacity units, should fit.

Be sure the equipment you purchase will meet your configuration needs. If you require a rackmount configuration and the vendor only sells freestanding, you have a problem.Tape drives are vulnerable to excesses of dust and dirt. Heat and humidity can affect not only the tape drive, but the autoloader and tapes as well. A clean, cool, dry environment is necessary to ensure the reliability of the tape automation.

Consider tape accessibility. Some units support bins that let you add and remove tapes in bulk, but some offer only one-at-a-time access. If you frequently take tapes off-site or add expired backup tapes to the library, for example, look for an autoloader that provides easy access to the tapes.

You also need to weigh the availability of connection technology. Some autoloaders come in a fixed configuration, usually SCSI or Fibre Channel, while others have I/O slots that will let you upgrade to different forms of connectivity in the future. If your company is contemplating a SAN, whether IP or Fibre Channel, hedge your bets with an autoloader that can be upgraded to handle either option.

Security is a concern, too. Some autoloaders have locking front panels for tape access and some require passwords for control-panel access. Invest in a product with the right level of security for your organization.

And don't forget ease of use. It may seem insignificant, but if it's a pain to access the tapes, people will avoid using the autoloader. Make sure the unit can be navigated by any IT person without any special training.What's New?

One popular feature, a disk for D2D2T (disk-to-disk-to-tape) operations, is showing up in the newest tape autoloaders. With D2D2T, you use a disk as an intermediate step in tiered storage. To your backup software, a disk is no different than tape. However, backing up or transferring to a disk is much faster than doing the same to tape. You'll have the time, between backups, to get the data from the disk to tape. And you can do this without adding load to your production servers.

Another advantage of D2D2T is that you can restore your most recent backup from disk much faster than you can from tape. But if you're going to rely on disk to extend your backup window, factor in the expandability of that disk to account for your five-year data growth.

The real key to purchasing a tape autoloader is understanding your current needs and considering your future needs. An inaccurate projection leads to either an anemic autoloader or money wasted on a unit you will never fully utilize.

Steven J. Schuchart Jr. covers storage and servers for NETWORK COMPUTING. Write to him at sschuchart@ nwc.com.0