Redundant Array of Independent Disks, or RAID, is a method of keeping content on multiple hard disk drives concurrently. A RAID can be software or hardware based on the hard drives which are used - physical or logical ones, but what’s common between them is that they all operate as just a single unit where information is kept. The biggest advantage of employing a RAID is redundancy because the information on all of the drives will be the same at all times, so even in the event that one of the drives fails for whatever reason, the info will still be present on the rest of the drives. The overall performance is also better because the reading and writing processes can be split between multiple drives, so a single one won't be overloaded. There're different types of RAIDs where the performance and fault tolerance can vary depending on the particular setup - whether info is written on all the drives in real time or it's written on a single drive and then mirrored on another, the number of drives are used for the RAID, etcetera.