RAID, or Redundant Array of Independent Disks, is a technology of saving data on several hard disk drives which function together as one single logical unit. The drives can be physical or logical i.e. in the latter case one single drive is divided into different ones via virtualization software. In either case, the very same data is saved on all of the drives and the basic advantage of employing such a setup is that in the event that a drive fails, the data will remain available on the remaining ones. Having a RAID also enhances the overall performance since the input and output operations will be spread among a number of drives. There are several kinds of RAID depending on how many drives are used, whether writing is done on all of the drives in real time or just on one, and how the info is synced between the drives - whether it is written in blocks on one drive after another or it is mirrored from one on the others. All of these factors indicate that the error tolerance and the performance between the different RAID types may vary.