Redundant Array of Independent Disks, or RAID, is a way of keeping content on several hard drives at the same time. A RAID might be software or hardware depending on the hard drives that are used - physical or logical ones, still what’s common between them is the fact that they all perform as a single unit where information is stored. The main advantage of employing a RAID is redundancy because the data on all drives will be exactly the same all of the time, so even in case some drive fails for whatever reason, the data will still be present on the remaining drives. The general performance is also better as the reading and writing processes could be split between multiple drives, so a single one will never be overloaded. There're different sorts of RAIDs where the performance and fault tolerance may differ depending on the particular setup - whether info is written on all drives real-time or it is written on one drive and then mirrored on another, what amount of drives are used for the RAID, etcetera.