RAID, or Redundant Array of Independent Disks, is a technology for saving data on several hard disks which operate together as one single logical unit. The drives can be physical or logical i.e. in the aforementioned case a single drive is divided into separate ones through virtualization software. In either case, the very same info is stored on all the drives and the key advantage of using such a setup is that in case a drive breaks down, the data shall still be available on the other ones. Using a RAID also enhances the overall performance because the input and output operations will be spread among several drives. There are several kinds of RAID based on how many hard drives are used, whether writing is performed on all the drives in real time or just on a single one, and how the data is synchronized between the hard drives - whether it's written in blocks on one drive after another or all of it is mirrored from one on the others. All of these factors mean that the fault tolerance as well as the performance between the various RAID types could differ.