Quantum DLT 2000 Handbook page 87

Improved data security and availability. Backups become auto-
matic, and backups are never missed. Data is secure and available
at a moment's notice.
Seamless disaster recovery. With a two-drive system, a complete
copy of a full backup can be made at the same time the primary
copy is running. Disaster recovery becomes almost effortless. It is
still necessary to test disaster recovery procedures on a regular
basis, but you'll know the data is secure.
Stacker, Autoloader, or Library?
The primary difference among tape automation systems is in the
way they handle data backup and access management. Stackers,
sometimes referred to as autoloaders, were the first tape automa-
tion products for small and mid-size IS operations. These systems
typically have one drive, and tapes are inserted and removed by the
system's mechanical picker, sometimes called an elevator, in
sequential order. So, for instance, if a stacker is set up to perform a
full backup of a database, the system would begin with tape "0"
and continue inserting and removing tapes until the backup was
completed, or the supply of cartridges exhausted.
An autoloader, again, has one drive, but has the added capability of
providing any tape in its magazine upon request. This ability to
randomly select tapes makes autoloaders appropriate for small-
scale network backup and near on-line storage applications.
Libraries offer the same type of functionality as autoloaders, but
are often equipped with multiple drives for handling large-scale
network backup, near on-line access, user-initiated file recovery,
and the ability to serve multiple users and multiple hosts simulta-
neously. On large libraries, multiple robotic mechanisms may also
be employed to improve system response time.
QUANTUM DLTtape HANDBOOK 8.7