The "I" in "RAID" stands for Inexpensive (even though it
sometimes rendered as Independent). This seems somewhat puzzling, since it is
only recently that RAID has begun to become popular on inexpensive IDE/ATA hard
disks--high-end SCSI disks are still the primary domain of RAID, and more often than not,
RAID arrays are constructed of some of the fastest drives on the planet. The reason for
the term "inexpensive" is that RAID is designed to use regular hard
disks, as opposed to proprietary, special hard disks. This is in fact a major reason why
it is so appealing. Before RAID, to get high performance or fault tolerance required the
purchase of specialized, very expensive drives. RAID lets you get those benefits while
using off-the-shelf drives.
Perhaps ironically, hard disks today are becoming downright inexpensive period, not
just when compared to proprietary solutions (which RAID has caused to all but disappear
from the market). This has fueled the RAID phenomenon and caused more and more RAID
systems to be created using disks of all pricing levels.
While RAID arrays use standard hard disks, that doesn't mean that you can just pick
"any old drives" you find kicking around and make a successful RAID array out of
them. There are a number of requirements that must be considered when choosing drives
(beyond the obvious, such as choosing drives matching the interface
of your controller implementation!) In this section, I will discuss factors such as drive
size, number of drives and how to choose specific units, along with taking a look at how
to meet the "needs" of your drives in terms of power, enclosures and cabling.
Next: Number of Drives
