RAID, which stands short for Redundant Array of Independent Disks, is a software or hardware storage virtualization technology which enables a system to take advantage of multiple hard drives as a single logical unit. In other words, all of the drives are used as one and the information on all of them is the same. This type of a configuration has two major advantages over using just a single drive to store data - the first one is redundancy, so in the event that one drive breaks down, the information will be accessible from the remaining ones, and the second is better performance since the input/output, or reading/writing operations will be distributed among multiple drives. You can find different RAID types depending on what number of drives are employed, whether reading and writing are both handled from all the drives simultaneously, whether data is written in blocks on one drive after another or is mirrored between drives in the same time, etc. Based on the particular setup, the fault tolerance and the performance vary.