Quantum DLT 2000 Handbook page 100

Surprisingly, HSM systems are not proliferating as rapidly as origi-
nally expected. This is due in large part to the drop in price and
increased capacity of today's disk drives. In addition, many library
and autoloader tape systems can perform many of the functions
that are typically associated with HSM systems. Libraries and
autoloaders can provide vast amounts of near on-line storage,
unattended access for users, and fast backups. HSM systems vary
in features and capabilities; however, many allow for the hot swap-
ping of components such as power supplies, drives, and cooling
fans without shutting the system down.
Virtual Tape
In many organizations, while applications are growing more data
intensive and more time critical, the time and resources available
for system management are diminishing. In situations in which
very large volumes of data must be backed up in very short win-
dows of time, this situation has reached a crisis – even though
these organizations are already taking advantage of high speed tape
drives, probably running in multi-streaming mode. It is in these
circumstances that virtual tape is most likely to be an option.
Virtual tape is an emerging storage strategy that, like HSM, uses
multiple storage technologies to achieve performance goals. The
basic concept of virtual tape is that backups can be made dramati-
cally faster by using high speed hard disk storage for a part of the
backup system. Most of the system's backup capacity is still in a
tape library or libraries, but part of it is in the form of hard disk
drives, most likely a RAID unit. This disk capacity, however, pre-
sents itself to the system, not as a hard disk, but as a "virtual" tape
unit. This means the system can take advantage of the speed of the
hard disk, while still using all the existing backup software and
procedures; it is as if there is a super fast tape drive or library in
the system. While hard disk is a relatively small part of the total
QUANTUM DLTtape HANDBOOK 9.7