RAID, or Redundant Array of Independent Disks, is a technology for saving data on a number hard disk drives which operate together as a single logical unit. The drives could be physical or logical i.e. in the latter case one single drive is divided into individual ones through virtualization software. In any case, exactly the same information is stored on all drives and the main benefit of employing such a setup is that if a drive breaks down, the data will remain available on the other ones. Employing a RAID also enhances the performance because the input and output operations will be spread among a number of drives. There are several types of RAID based on how many hard disks are used, whether writing is done on all the drives in real time or just on a single one, and how the info is synced between the drives - whether it's recorded in blocks on one drive after another or it is mirrored from one on the others. These factors show that the fault tolerance as well as the performance between the various RAID types may differ.