RAID, which is an acronym of Redundant Array of Independent Disks, is a software or hardware storage virtualization technology that makes it possible for a system to use many hard drives as a single logical unit. Simply put, all drives are used as one and the data on all of them is identical. This kind of a configuration has 2 major advantages over using a single drive to store data - the first one is redundancy, so in case one drive fails, the information will be accessed from the remaining ones, and the second one is better performance as the input/output, or reading/writing operations will be distributed among a number of drives. There're different RAID types depending on the number of drives are employed, whether reading and writing are both performed from all drives at the same time, if data is written in blocks on one drive after another or is mirrored between drives in the same time, etc. Depending on the exact setup, the fault tolerance and the performance may vary.