Redundant Array of Independent Disks, or RAID, is a method of keeping content on a number of hard disk drives simultaneously. A RAID could be software or hardware depending on the drives which are used - physical or logical ones, yet what’s common between them is the fact that they all perform as just a single unit where info is stored. The main advantage of using a RAID is redundancy because the information on all drives will be the same all of the time, so even in case some drive fails for whatever reason, the data will still be present on the rest of the drives. The overall performance is also better as the reading and writing processes will be split between various drives, so a single one won't be overloaded. There are different kinds of RAIDs where the functionality and fault tolerance can vary according to the exact setup - whether data is written on all of the drives in real time or it's written on a single drive and afterwards mirrored on another, what amount of drives are used for the RAID, etcetera.