RAID, or Redundant Array of Independent Disks, is a technology of saving data on a number hard drives which work together as a single logical unit. The drives can be physical or logical i.e. in the latter case one drive is divided into different ones using virtualization software. Either way, exactly the same information is kept on all drives and the main advantage of employing such a setup is that in the event that a drive breaks down, the data shall still be available on the remaining ones. Employing a RAID also improves the overall performance since the input and output operations will be spread among several drives. There are several types of RAID depending on how many drives are used, whether writing is done on all drives in real time or just on one, and how the information is synchronized between the hard drives - whether it is written in blocks on one drive after another or all of it is mirrored from one on the others. These factors indicate that the error tolerance as well as the performance between the various RAID types could differ.