"KILLS - BUGS - DEAD!"
-- TV commercial for RAID bug spray
There are many applications, particularly in a business environment, where there are
needs beyond what can be fulfilled by a single hard disk, regardless of its size,
performance or quality level. Many businesses can't afford to have their systems go down
for even an hour in the event of a disk failure; they need large storage subsystems with
capacities in the terabytes; and they want to be able to insulate themselves from hardware
failures to any extent possible. Some people working with multimedia files need fast data
transfer exceeding what current drives can deliver, without spending a fortune on
specialty drives. These situations require that the traditional "one hard disk per
system" model be set aside and a new system employed. This technique is called Redundant
Arrays of Inexpensive Disks or RAID. ("Inexpensive" is sometimes
replaced with "Independent", but the former term is the one that was used when
the term "RAID" was first coined by the researchers at the University of
California at Berkeley, who first investigated the use of multiple-drive arrays in 1987.)
The fundamental principle behind RAID is the use of multiple hard disk drives in an
array that behaves in most respects like a single large, fast one. There are a number of
ways that this can be done, depending on the needs of the application, but in every case
the use of multiple drives allows the resulting storage subsystem to exceed the capacity,
data security, and performance of the drives that make up the system, to one extent or
another. The tradeoffs--remember, there's no free lunch--are usually in cost and
complexity.
Originally, RAID was almost exclusively the province of high-end business applications,
due to the high cost of the hardware required. This has changed in recent years, and as
"power users" of all sorts clamor for improved performance and better up-time,
RAID is making its way from the "upper echelons" down to the mainstream. The
recent proliferation of inexpensive RAID controllers that work with consumer-grade IDE/ATA
drives--as opposed to expensive SCSI units--has increased interest in RAID dramatically.
This trend will probably continue. I predict that more and more motherboard manufacturers
will begin offering support for the feature on their boards, and within a couple of years
PC builders will start to offer systems with inexpensive RAID setups as standard
configurations. This interest, combined with my long-time interest in this technology, is
the reason for my recent expansion of the RAID coverage on this site from one page to 80.
Unfortunately, RAID in the computer context doesn't really kill bugs dead. It can, if
properly implemented, "kill down-time dead", which is still pretty good.
Next: Why Use RAID? Benefits and Costs, Tradeoffs and Limitations
