Redundant Array of Independent Disks, or RAID, is a way of storing content on multiple hard drives at the same time. A RAID can be software or hardware depending on the drives that are used - physical or logical ones, still what’s common between them is that they all operate as one single unit where info is saved. The key advantage of employing a RAID is redundancy because the information on all of the drives will be the same all of the time, so even in the event that a drive fails for whatever reason, the data will still be present on the remaining drives. The general performance is also enhanced because the reading and writing processes will be split between a number of drives, so a single one will not be overloaded. There're different types of RAIDs where the effectiveness and fault tolerance could differ depending on the exact setup - whether information is written on all drives in real time or it is written on one drive and afterwards mirrored on another, the number of drives are used for the RAID, etc.