RAID, which is an acronym of Redundant Array of Independent Disks, is a software or hardware storage virtualization technology that permits a system to employ a number of hard drives as one single logical unit. Put simply, all of the drives are used as one and the info on all of them is identical. This type of a setup has two key advantages over using a single drive to save data - the first is redundancy, so in the event that one drive doesn't work, the data will be accessed through the remaining ones, and the second is better performance since the input/output, or reading/writing operations will be spread among a number of drives. There're different RAID types in accordance with what amount of drives are used, whether reading and writing are both handled from all drives concurrently, whether data is written in blocks on one drive after another or is mirrored between drives in the same time, etc. According to the exact setup, the error tolerance and the performance may vary.