Redundant Arrays of Inexpensive (Independent) Disks or RAID was first coined by researchers at the University of California at Berkeley. The fundamental principle behind RAID is that it allows a collection of individual disks to behave as one larger, faster, and more reliable disk. Thus capacity, performance, security, and reliability of the disk subsystems exceed that of its constituents. Once almost exclusively the province of expensive SCSI disks, RAID has gained in popularity with the steady increase in the affordability and performance of ATA drives. How disks are accessed, written to and read from results in many different implementation of RAID, referred to as RAID levels, that each have advantages and also their associated costs. Differentiation between these different levels comes in the trade offs they make in the three dimensions of reliability/fault tolerance, performance/capacity, and cost. Please also note that no system is totally and utterly fool proof. Backups remain critical even when RAID is used.
|Efficiency||100%||50%||Good(1 drives per set)||Good(2 drives per set)||50%||Good||Fair|
|Fault Tolerance||None||Excellent||Good||Very Good||Excellent||Good||Very Good|
|Availability||Low||Excellent||Good||Very Good||Excellent||Good||Very Good|
|Random Read||Good||Fair||Fair – Good||Fair – Good||Fair – Good||Very Good||Very Good|
|Sequential Read||Very Good||Fair||Very Good||Very Good||Very Good||Very Good||Very Good|
|Sequential Write||Very Good||Fair||Good||Good||Very Good||Very Good||Very Good|
Table 1: Comparing attributes of different RAID levels