RAID, or Redundant Array of Independent Disks, is a technology for keeping data on multiple hard drives which work together as one single logical unit. The drives could be physical or logical i.e. in the aforementioned case a single drive is split into different ones through virtualization software. In any case, the same data is stored on all the drives and the main benefit of employing such a setup is that if a drive breaks down, the data shall still be available on the other ones. Employing a RAID also boosts the overall performance since 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 drives in real time or just on a single one, and how the data is synced between the hard drives - whether it is recorded in blocks on one drive after another or it is mirrored from one on the others. These factors imply that the error tolerance as well as the performance between the various RAID types may vary.