RAID, or Redundant Array of Independent Disks, is a technology of saving data on several hard disk drives that operate together as one single logical unit. The drives can be physical or logical i.e. in the latter case a single drive is divided into separate ones through virtualization software. Either way, the very same data is kept on all the drives and the key benefit of employing this kind of a setup is that in case a drive stops working, the data shall still be available on the remaining ones. Employing a RAID also boosts the overall performance as the input and output operations will be spread among a couple of drives. There are several kinds of RAID depending on how many hard drives are used, whether writing is performed on all drives in real time or just on a single one, and how the information is synchronized between the drives - whether it is written in blocks on one drive after another or it is mirrored from one on the others. These factors mean that the error tolerance as well as the performance between the various RAID types could differ.