RAID, which is an acronym of Redundant Array of Independent Disks, is a software or hardware storage virtualization technology that enables a system to take advantage of multiple hard drives as a single logical unit. Put simply, all the drives are used as one and the info on all of them is the same. This kind of a setup has two major advantages over using a single drive to store data - the first is redundancy, so in the event that one drive doesn't work, the info will be accessible through the remaining ones, and the second is better performance because the input/output, or reading/writing operations will be distributed among several drives. You can find different RAID types in accordance with how many drives are used, whether reading and writing are both executed from all the drives simultaneously, whether data is written in blocks on one drive after another or is mirrored between drives in the same time, and so on. Depending on the exact setup, the error tolerance and the performance vary.