RAID, or Redundant Array of Independent Disks, is a technology for saving data on multiple hard disks that operate together as a single logical unit. The drives can be physical or logical i.e. in the aforementioned case one single drive is split into individual ones using virtualization software. In either case, exactly the same data is kept on all the drives and the main advantage of using such a setup is that in case a drive fails, the data will remain available on the other ones. Having a RAID also boosts the performance as the input and output operations will be spread among a few drives. There are several kinds of RAID based 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 data is synchronized between the drives - whether it's recorded in blocks on one drive after another or it is mirrored from one on the others. These factors suggest that the fault tolerance as well as the performance between the various RAID types can differ.