Backing Up with Tape Drives: Security Is What Counts

DLT, SDLT

A DLT or an SDLT cartridge has only one bobbin around which the tape is wound. At the end is a large loop. The tape is pulled from the cartridge when it's entered and wound around a reel in the drive. The mechanism with several guide rollers functions such that no roller touches the tape on the data side, only on the reverse. Only the read and write head has contact with the tape's data side. Tape drives in this category are expensive, with prices starting at around $4000.

LTO

This technology functions in much the same way as the DLT drives. The somewhat smaller cartridge also has a reel on which the 600 meters of tape are wound. When inserted in the streamer, the tape is drawn out and gradually wound around a reel inside the drive. A 4 kB memory chip is integrated in every tape for seamless communication. The drive stores the tape index here, as well as various parameters such as serial number, date of first use, or history. The devices start at $4500 (Seagate).

SLR

Tandberg's SLR (Scalable Linear Recording) technology handles capacities of up to 50 GB and a data rate of 5 MB per second. The cartridges with solid metal base plates are very similar to the QIC tapes, and the remaining technology owes a lot to QIC drives. SLR uses normal linear tracks in which four tracks are written at the same time. Because of this data density, SLR also uses PRML technology.

VXA

VXA technology puts the emphasis on data security and tape readability when drives are changed or environmental changes occur (e.g., humidity, cold). To achieve this, two pairs of heads on a rotating drum (Helical Scan Technology) work in tandem when writing. The first head writes a track and the second reads it back to test reliability. If an error occurs, the track is rewritten.

Two heads also work together during the read process, reading the same track in close alignment. If this is not successful, all four heads are used. This means that tracks can still be used, even if they are severely tilted. The ExaByte VXA-2 drive in this group costs $999.