Redundant Array of Independent Disks, or RAID, is a way of keeping content on multiple hard disk drives simultaneously. A RAID could be software or hardware depending on the hard drives which are used - physical or logical ones, however what is common between them is that they all operate as just one single unit where information is saved. The top advantage of using a RAID is redundancy because the info on all the drives shall be identical at all times, so even if a drive fails for whatever reason, the data will still be present on the remaining drives. The overall performance is also better as the reading and writing processes could be split between different drives, so a single one will never be overloaded. There are different sorts of RAIDs where the performance and fault tolerance may vary based on the particular setup - whether your data is written on all of the drives real-time or it's written on one drive and afterwards mirrored on another, what amount of drives are used for the RAID, and many others.