Despite the improved reliability of recent hard drives, moving parts have a finite lifespan. Some day your computer's drive will crash, taking your photographs with it -- unless you back up its contents zealously. One convenient and reasonably priced solution is this dual-drive RAID (redundant array of independent disks). The Guardian MAXimus continuously "mirrors" your data to two separate drives, writing two identical volumes. If one drive fails, the RAID's status LEDs warn you, even as it continues to write data to the second. Pull the bad drive from the Guardian's case, slip in a new one, and the unit fully restores your data from the backup to the replacement. And it does so quickly: drives are 7200rpm Seagate Barracuda SATAs with 32MB or 64MB memory caches, supported by FireWire 400, FireWire 800, and USB 2.0 connections. The new unit is available in capacities from 250GB to 1TB, in addition to a superfast 10,000rpm 150GB version and driveless case for those who want to choose their own drives. About $420 (400GB).