RAID, which is short for Redundant Array of Independent Disks, is a software or hardware storage virtualization technology that makes it possible for a system to take advantage of multiple hard drives as a single logical unit. Put simply, all the drives are used as one and the data on all of them is the same. This type of a configuration has two major advantages over using a single drive to save data - the first is redundancy, so in the event that one drive breaks down, the data will be accessed from the remaining ones, and the second 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, if reading and writing are both handled from all of the drives simultaneously, if data is written in blocks on one drive after another or is mirrored between drives in the same time, and so on. According to the particular setup, the error tolerance and the performance may differ.