There are all kinds of storage device that can be used to back up data, from high density super-floppy disks to DVD drives. But when it come to providing the speed, capacity and reliability needed to protect shared network data, most companies choose one of the automated tape storage applications have emerged in recent years:
- Tape Libraries: The increasing demands being placed on client servers require provisions for off-line data storage with automated access and control. A tape library is a high-capacity data storage system for storing, retrieving, reading and writing multiple magnetic tape cartridges. It is essentially two pieces of hardware: the tape drive itself plus a set of robotics. The latter provides the required capacity, picking up tape cartridges from built in storage racks and loading them into the drive as and when required by the backup software. Similarly, the autoloader then removes the cartridges when they’re full, storing them until they’re next needed. Tape libraries are available for half-inch, QIC, Travan,DAT and 8mm tape cartridges. Smaller units can have several drives for simultaneous reading and writing and may hold from a handful to several hundred cartridges. Large units can have hundreds of drives and hold several thousand cartridges. Tape Library devices are referred to as near on-line (or near-line) because they are not as fast as on-line hard disks.
- Tape Arrays: Tape arrays are based on technology borrowed from disk-based RAID subsystems. The idea isn’t new, but until recently arrays did not provide much performance benefit over single drives. They have now become a practical option for midrange storage. Arrays are based on special controllers that can stripe data across multiple drives in parallel, as opposed to the slow sequential access on a single device. Tape array vendors claim that an array with four drives will provide a fourfold performance improvement over a stand-alone drive. For extra fault tolerance, most tape arrays can be configured with a parity drive. The downside is a decrease in overall throughput gains.
- Hierarchical Storage Management: HSM applications are designed to minimise storage costs while optimising performance. They achieve this by combining multiple storage media such as magnetic disk, optical disk, and tape into a single logical unit, and transparently migrating data between media based on access frequency.