RAID levels differ in terms of the controller required to implement them. In general,
simple controllers implement simple RAID levels, while more complex RAID levels require
more sophisticated (read: expensive) controllers. Some levels don't require a dedicated
controller at all, functioning acceptably using operating system or other software to manage the array (albeit at a performance
price).
The simplest RAID levels, often supported by software RAID or low-end controllers,
include RAID 0, RAID 1, and RAID 0+1 or 1+0 (though many low-end controllers only support
one or the other, not both.) Some lower-end controllers include support for the popular
RAID 5 level, and so do some software RAID implementations, but at a rather severe penalty
in terms of performance and advanced features. RAID levels
3, 4, 6 and 7, and the other more esoteric multiple RAID levels such as RAID 53 and RAID
30, usually require more capable controllers. RAID 2 is complex enough that it requires
special, proprietary hardware; it has for this reason all but disappeared from the market.
Next: Hard Disk Requirements
