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important feature of the industry-leading tape libraries. There is currently
only one tape library manufacturer that provides an interchange mechanism
between libraries to allow cartridges to be mounted in tape drives existing in
separate libraries connected via the passthrough port. This is an extremely
useful feature in a mixed media multitape library environment in that it pre-
vents the need to directly manage the usage of tapes in drives.
Experiences at most High-Performance Computing centers with both
commodity- and enterprise-class tape drives support the claim that enterprise-
class tape drives do actually exhibit fewer problems in terms of placing user
data at risk than the commodity drives.
1.4.3 Commodity Tape Technology
For as long as computer technology has existed in the home, there has ex-
isted some form of commodity tape intended for general consumer use. There
are several types of tape used in electronics, with the most common being
magnetic tape.
In the 1980s and 1990s commodity magnetic tape was primarily built
around 8 mm tape that was mostly used to handle backups of the machine to
which they were attached. In the mid-to late 1990s the commodity tape drive
market opened up with the definition of a new kind of tape drive called LTO
that defined a new market sector called midrange tape.
The linear tape-open (LTO) tape technology has a strong hold in the mar-
ketplace today primarily because of its low cost and relatively good perfor-
mance capabilities and large capacities. It was primarily intended for use with
backup applications where absolute assurance of no single point of failure or
data loss was not critical. This is due to the fact that backup data is a copy
of the original data and in general loses value over time. However, because
of its low cost and relatively good performance and capacity, the technology
has started to emerge as a viable option for the most data-intensive high-
performance computing centers especially for consideration in dual-copy or
the lowest tiers of storage in a hierarchical system. If used in a mass storage
system with archival storage requirements, most centers simply make multiple
copies of data retained on this technology.
The LTO specification has plans to release six generations or form factors
of tape. For LTO-6, the final version plans to provide 3.2 TB of data and a
speed of 270 MB/s. Currently, the LTO-4 drive is available and delivers 800
GB of data on a single cartridge and up to 120 MB/s data transfer speed.
In the last few years, several midrange tape libraries have emerged in the
market that are capable of handling the full spectrum of drives and tape tech-
nologies available. Several of these mid-range libraries are starting to adopt
features of the enterprise-class libraries, specifically redundant components,
ruggedized robotics, and expansion capabilities. They are excellent for appli-
cations that do not require scalability beyond the limits of the library.
