RAID, or Redundant Array of Independent Disks, is a technology for saving data on a number hard disks that function together as one logical unit. The drives could be physical or logical i.e. in the second case one single drive is split into separate ones through virtualization software. In any case, the same information is stored on all drives and the main benefit of employing such a setup is that in case a drive breaks down, the data shall still be available on the remaining ones. Having a RAID also enhances the performance since the input and output operations will be spread among a couple of drives. There are several types of RAID based on how many hard disks are used, whether writing is carried out on all of the drives in real time or just on one, and how the info is synchronized between the drives - whether it is recorded in blocks on one drive after another or all of it is mirrored from one on the others. These factors suggest that the fault tolerance as well as the performance between the various RAID types can differ.