PATA/SATA RAID

RAID is an acronym for redundant array of independent (or inexpensive) disks and was designed to improve the fault tolerance and performance of computer storage systems. RAID was developed at the University of California at Berkeley in 1987 and was designed so that a group of smaller, less expensive drives could be interconnected with special hardware and software to make them appear as a single larger drive to the system. By using multiple drives to act as one drive, increases in fault tolerance and performance could be realized.

Initially, RAID was conceived to simply enable all the individual drives in the array to work together as a single, larger drive with the combined storage space of all the individual drives, which is called a JBOD (Just a Bunch of Disks) configuration. Unfortunately, if you had four drives connected in a JBOD array acting as one drive, you would be four times more likely to experience a drive failure than if you used just a single larger drive. And because JBOD does not use striping, performance would be no better than a single drive either. To improve both reliability and performance, the Berkeley scientists proposed six levels (corresponding to different methods) of RAID. These levels provide varying emphasis on fault tolerance (reliability), storage capacity, performance, or a combination of the three.