RAID, or Redundant Array of Independent Disks, is a technology of keeping data on several hard disks which work together as one single logical unit. The drives can be physical or logical i.e. in the latter case one single drive is divided into independent ones using virtualization software. In any case, identical info is kept on all of the drives and the key benefit of employing this kind of a setup is that in case a drive breaks down, the data shall still be available on the other ones. Using a RAID also boosts the performance as the input and output operations will be spread among a few drives. There are several kinds of RAID based on how many drives are used, whether writing is carried out on all drives in real time or just on one, and how the info is synchronized between the hard drives - whether it is recorded in blocks on one drive after another or all of it is mirrored from one on the others. All of these factors indicate that the error tolerance and the performance between the various RAID types can differ.