RAID, or Redundant Array of Independent Disks, is a technology of keeping data on a number hard disk 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 via virtualization software. In any case, the same info is saved on all the drives and the key advantage of employing this kind of a setup is that in case a drive fails, the data shall still be available on the other ones. Using a RAID also enhances the overall performance as the input and output operations will be spread among a couple of drives. There are several kinds of RAID dependant upon how many hard drives are used, whether writing is carried out on all of the drives in real time or just on a single one, and how the info is synchronized between the drives - whether it is written in blocks on one drive after another or it is mirrored from one on the others. These factors show that the error tolerance as well as the performance between the various RAID types could differ.