RAID, or Redundant Array of Independent Disks, is a technology of saving data on several hard drives which function together as a single logical unit. The drives could be physical or logical i.e. in the aforementioned case a single drive is split into different ones using virtualization software. In any case, identical info is kept on all of the drives and the basic advantage of employing such a setup is that in case a drive fails, the data will still be available on the other ones. Having a RAID also improves the overall performance because the input and output operations will be spread among a couple of drives. There are several kinds of RAID dependant upon how many hard disks are used, whether writing is carried out on all the drives in real time or just on one, and how the info is synchronized between the drives - whether it is written in blocks on one drive after another or all of it is mirrored from one on the others. All of these factors imply that the fault tolerance as well as the performance between the different RAID types may vary.