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 employ a number of hard drives as a single logical unit. In other words, all drives are used as one and the information on all of them is identical. Such a setup has 2 key advantages over using just a single drive to store data - the first is redundancy, so in the event that one drive breaks down, the information will be accessed through the others, and the second one is improved performance since the input/output, or reading/writing operations will be distributed among multiple drives. There're different RAID types in accordance with the number of drives are used, whether reading and writing are both performed from all of the drives at the same time, whether data is written in blocks on one drive after another or is mirrored between drives in the same time, and so on. Depending on the exact setup, the error tolerance and the performance could differ.