Database Reference
In-Depth Information
being explored as a component for ultraecient composite (RAID) storage
devices such as Massive Arrays of Idle Disks (MAID).
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While enterprise-class storage devices have enjoyed a niche market in large-
scale storage solutions, they have been gradually supplanted over time by
consumer-grade devices that depend on assembly into hierarchical RAID de-
vices to match the reliability and performance of the enterprise-class devices.
Recent studies
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,
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have cast doubt on claims that enterprise-class disks of-
fer lower failure rates than their consumer-grade counterparts. Consequently,
enterprise-class RAID storage subsystems composed of consumer-grade SATA
disks are rapidly overtaking the enterprise market segment.
1.3.4 Future Trends
Magnetic disk technologies are faced with the theoretical limitation of super-
paramagnetism which proposes that as bit density is increased so must power
to the device in order to prevent spontaneous changes of data (e.g., a bit
flip) from occurring. Because this is a theoretical limitation, the actual limit
is not known and continues to change each time a manufacturer produces a
higher capacity disk. Several manufacturers are developing solutions to the
problem, but the main concern with the limitation is that solutions will come
at a significant increase in cost. This would have ramifications for the high-
performance computing sites that rely on squeezing ever increasing amounts
of storage into smaller spaces at a fixed cost.
1.4 Tape Storage
Tape has been the primary medium for oine storage since the 1980s. Mag-
netic disks or hard disk drives (HDD) are its primary competitor in terms
of capacity and data transfer capabilities. Through the early 1990s tape re-
mained slow and well behind disk drives in terms of performance, but well
ahead of disk in terms of capacity. Disk storage was still in the MBs of space,
and disk drives were a premium in terms of cost. In the early 1990s disk stor-
age became commonplace and extremely affordable as the number of personal
computers soared.
The key principles or advantages of tape storage that will continue to make
it a viable mass storage solution if not the primary mass storage solution
well into the future are that they are removable, extremely power ecient,
maximize GB/sq ft, and continue to offer a competitive price/GB. Like optical
storage, it is removable media. This fact allows tape to be an ideal solution
for offsite data requirements. Tape is also primarily used for system backups
because data can easily be exchanged between systems or stored separate from
the system to prevent risk from colocation with the primary data source. Tapes
