Lets get this out of the way first: Small- and midsize businesses need to have a regular backup routine for their servers. Copying a few key files to a CD every now and then wont cut it if your servers hard drive crashes, and the days of downtime and thousands of dollars youll burn as a recovery service tries (perhaps unsuccessfully) to resurrect your data will be an expensive lesson indeed.
Even with the decreasing cost of hard drives, which lets you put a second drive in a server to act as a backup, tape remains the storage medium of choice for businesses with moderate-to-large volumes of frequently changing data. Unlike mirrored drives, copies of data stored on tape can be easily kept off-site for added protection.
One of the newest midrange tape solutions is the Exabyte VXA-2. A proprietary technology, VXA-2 is a good replacement for the aging DDS tape technology, which appears to have reached its limits on capacity (36GB native, 72GB with compression per cartridge) and performance (210MB to 420MB per minute). VXA-2 can store up to 80GB (160GB compressed) per cartridge, and it reads and writes data at 360MB to 720MB per minute. If thats still not enough capacity or performance for your needs, youll want to consider the higher-speed (and pricier) LTO, AIT-3, and SDLT tape technologies (see “Tape It to the Limit,” March 11).
VXA-2 is unlike any other tape technology in that it reads and writes data on a packet basis rather than reading and writing large blocks of data along linear or helical tracks. VXA-2 drives can also adjust tape speed to match the transfer rate of the host. This avoids back-hitching operations that can occur with other tape technologies when data flow is interrupted and the tape is forced to stop, back up, and restart. Back-hitching not only decreases performance but can also accelerate media wear.
With VXA-2 technology, two head pairs (each pair containing one read and one write head, totaling four heads) are contained on a rotating drum and are arranged as leading and trailing pairs. The heads sweep across the width of the moving tape at an angle. (See www.exabyte.com/technology/vxa/tour for animations that describe the drives operation.)
During a read operation, all four heads perform read operations, with the leading head of a pair reading the data and the trailing head verifying it. During writes, the leading head writes and trailing head verifies.
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