Storage Area Network: Architecture

Tape Drives, Libraries and Autoloaders

One of the purposes of a SAN is to allow for network backups. Ideally, these backups are configured so that they do not occur on a primary LAN; this could negatively impact the LAN's performance. Because the backup is handled by the SAN, precious LAN bandwidth is not used. Magnetic tape drive units provide the ability to back up large amounts of data. These backup devices can take the form of single-tape or multi-tape backup units. Based on their limited storage capacity, single-tape backup units are not considered appropriate for a SAN. Multi-tape backup units, in the form of autoloaders or tape libraries, provide the capacity required to back up the large volumes of data stored in a SAN environment.

Tape Libraries

Most tape backups that occur under SAN environments utilize tape libraries. Tape libraries are self-contained, fully automated tape cartridge systems that can accommodate multiple tape drives. Tape libraries contain robotic arms that move cartridges to and from storage cells. An electronic eye, usually attached to the robotics, reads bar-coded labels on the tapes to identify them.

Autoloaders

SAN environments can also utilize an autoloader for tape backup. An autoloader is very similar to a tape library. Generally autoloaders are fully automated, containing a single tape drive, and holding no more than 10 tapes. A small robotic arm shuffles the tapes around.

Because tape libraries feature much greater capacities, autoloaders are rarely used in a SAN environment. Autoloaders are more effective in non-SAN environments.