Redundant Array of Independent Disks, or RAID, is a method of storing content on multiple hard disk drives at the same time. A RAID could be software or hardware depending on the drives which are used - physical or logical ones, still what’s common between them is the fact that they all operate as one single unit where data is saved. The key advantage of using a RAID is redundancy since the data on all the drives will be exactly the same at all times, so even in the event that some drive fails for some reason, the info will still be present on the other drives. The overall performance is also enhanced as the reading and writing processes can be split between various drives, so a single one will never be overloaded. There are different kinds of RAIDs where the functionality and fault tolerance may differ based on the exact setup - whether your data is written on all drives real-time or it's written on one drive and after that mirrored on another, what number of drives are used for the RAID, etcetera.