Redundant Array of Independent Disks, or RAID, is a way of saving content on multiple hard disk drives at the same time. A RAID might be software or hardware depending on the drives that are used - physical or logical ones, still what is common between them is that they all perform as just a single unit where data is saved. The top advantage of using a RAID is redundancy since the info on all drives shall be identical all the time, so even in the event that some drive fails for whatever reason, the data will still be available on the rest of the drives. The general performance is also enhanced because the reading and writing processes could be split between multiple drives, so a single one will not be overloaded. There are different sorts of RAIDs where the functionality and fault tolerance can vary according to the specific setup - whether info is written on all drives in real time or it is written on a single drive and afterwards mirrored on another, what number of drives are used for the RAID, and so on.