RAID, which stands short for Redundant Array of Independent Disks, is a software or hardware storage virtualization technology which permits a system to use multiple hard drives as a single logical unit. To put it differently, all of the drives are used as one and the information on all of them is identical. Such a configuration has 2 major advantages over using just a single drive to keep data - the first one is redundancy, so in case one drive doesn't work, the information will be accessed from the others, and the second is improved performance because the input/output, or reading/writing operations will be distributed among several drives. There are different RAID types in accordance with how many drives are employed, whether reading and writing are both done from all drives simultaneously, if data is written in blocks on one drive after another or is mirrored between drives in the same time, etcetera. According to the particular setup, the fault tolerance and the performance may differ.