RAID, which is short for Redundant Array of Independent Disks, is a software or hardware storage virtualization technology which permits a system to take advantage of many hard drives as a single logical unit. In other words, all drives are used as one and the info on all of them is identical. This type of a setup has 2 major advantages over using a single drive to store data - the first is redundancy, so in the event that one drive breaks down, the data will be accessible through the others, and the second one is improved performance since the input/output, or reading/writing operations will be spread among several drives. There're different RAID types based on the number of drives are used, 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, and many others. Based on the particular setup, the error tolerance and the performance may differ.