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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.

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