RAID, which stands short for Redundant Array of Independent Disks, is a software or hardware storage virtualization technology that permits a system to use a number of hard drives as a single logical unit. Simply put, all drives are used as one and the info on all of them is identical. This type of a configuration has two major advantages over using just a single drive to save data - the first is redundancy, so in case one drive fails, the information will be accessible through the others, and the second is improved performance because the input/output, or reading/writing operations will be spread among a number of drives. You can find different RAID types in accordance with what number of drives are employed, whether reading and writing are both handled from all of the drives concurrently, 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 vary.