RAID, which stands short for Redundant Array of Independent Disks, is a software or hardware storage virtualization technology that makes it possible for a system to use several hard drives as a single logical unit. To put it differently, all the drives are used as one and the data on all of them is the same. This kind of a setup has 2 key advantages over using just a single drive to save data - the first is redundancy, so if one drive doesn't work, the info will be accessible through the others, and the second is improved performance since the input/output, or reading/writing operations will be distributed among several drives. You can find different RAID types based on what amount of drives are used, if reading and writing are both performed from all 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. Determined by the exact setup, the fault tolerance and the performance may differ.