RAID, which is an acronym of Redundant Array of Independent Disks, is a software or hardware storage virtualization technology which makes it possible for a system to take advantage of a number of hard drives as a single logical unit. To put it differently, all of the drives are used as one and the info on all of them is identical. This kind of a setup has two key advantages over using just a single drive to store data - the first one is redundancy, so in the event that one drive stops working, the data will be accessible through the remaining ones, and the second is better performance because the input/output, or reading/writing operations will be distributed among multiple drives. You can find different RAID types based on what amount of drives are employed, if reading and writing are both done from all 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. Determined by the exact setup, the error tolerance and the performance may differ.