RAID, or Redundant Array of Independent Disks, is a technology of storing data on a number hard disks that operate together as one logical unit. The drives can be physical or logical i.e. in the latter case one drive is split into different ones using virtualization software. In any case, the very same information is kept on all the drives and the main advantage of using this kind of a setup is that if a drive stops working, the data will still be available on the remaining ones. Employing a RAID also improves the performance as the input and output operations will be spread among a number of drives. There are several types of RAID depending on how many hard disks are used, whether writing is carried out on all drives in real time or just on one, and how the information is synchronized between the hard drives - whether it's recorded 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 various RAID types can vary.