RAID, which is an acronym of Redundant Array of Independent Disks, is a software or hardware storage virtualization technology which enables a system to use many hard drives as one single logical unit. To put it differently, all drives are used as one and the info on all of them is identical. Such a setup has two huge 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 one is better performance since the input/output, or reading/writing operations will be distributed among a number of drives. There're different RAID types in accordance with how many drives are employed, whether reading and writing are both handled from all of the drives simultaneously, whether data is written in blocks on one drive after another or is mirrored between drives in the same time, and many others. According to the exact setup, the error tolerance and the performance may differ.