RAID, which is short for Redundant Array of Independent Disks, is a software or hardware storage virtualization technology which enables a system to take advantage of many hard drives as a single logical unit. To put it differently, all drives are used as one and the data on all of them is the same. This type of a setup has two key advantages over using just a single drive to save data - the first one is redundancy, so in the event that one drive stops working, the data will be accessible from the remaining ones, and the second one is better performance because the input/output, or reading/writing operations will be distributed among a number of drives. There are different RAID types in accordance with how many drives are employed, whether reading and writing are both executed from all of the 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, etc. Determined by the exact setup, the error tolerance and the performance may differ.