RAID, or Redundant Array of Independent Disks, is a technology for saving data on several hard disks which operate together as a single logical unit. The drives can be physical or logical i.e. in the second case one drive is divided into individual ones through virtualization software. Either way, the same information is kept on all drives and the basic advantage of using this kind of a setup is that in the event that a drive stops working, the data will still be available on the remaining ones. Employing a RAID also boosts the overall performance since the input and output operations will be spread among a few drives. There are several kinds of RAID depending on how many hard drives are used, whether writing is carried out on all the drives in real time or just on one, and how the information is synced between the hard drives - whether it's recorded in blocks on one drive after another or all of it is mirrored from one on the others. All these factors suggest that the fault tolerance and the performance between the different RAID types can vary.