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 a number of hard drives as a single logical unit. To put it differently, all of the drives are used as one and the information on all of them is the same. This kind of a configuration has two huge advantages over using just a single drive to keep data - the first is redundancy, so in the event that one drive stops working, the info will be accessed through the remaining ones, and the second is improved performance since the input/output, or reading/writing operations will be distributed among a number of drives. You can find different RAID types depending on what number of drives are used, if 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. According to the particular setup, the error tolerance and the performance may differ.