RAID, which is short for Redundant Array of Independent Disks, is a software or hardware storage virtualization technology that allows a system to use a number of hard drives as one single logical unit. In other words, all drives are used as one and the info on all of them is the same. Such a setup has two key advantages over using a single drive to store data - the first is redundancy, so in case one drive stops working, the info will be accessible from the remaining ones, and the second one is better performance since the input/output, or reading/writing operations will be distributed among different drives. There are different RAID types depending on how many drives are employed, whether reading and writing are both handled from all 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. Based on the exact setup, the fault tolerance and the performance may vary.