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.
|
|
Level 0 |
Level 1 |
Level 5 |
Level 10 |
Level 50 |
|
Efficiency |
100% |
50% |
Good (~75%) |
50% |
Good (~75%) |
|
Fault Tolerance |
None |
Very Good |
Good |
Excellent |
Good-Very Good |
|
Availability |
Low |
Very Good |
Good-Very Good |
Excellent |
Very Good/Exc. |
|
Random Read |
Very Good |
Good |
Very Good-Exc. |
Very Good-Exc. |
Very Good-Exc. |
|
Random Write |
Very Good |
Good |
Fair |
Good-Very Good |
Good |
|
Sequential Read |
Very Good-Exc. |
Fair |
Good-Very Good |
Very Good-Exc. |
Very Good |
|
Sequential Write |
Very Good |
Good |
Fair to Good |
Good-Very Good |
Good |
Table 1: Comparing attributes of different RAID levels
