Redundant Array of Independent Disks, or RAID, is a way of saving content on a number of hard disks simultaneously. A RAID could be software or hardware based on the HDDs which are used - physical or logical ones, yet what’s common between them is that they all function as just a single unit where data is stored. The main advantage of using a RAID is redundancy since the info on all of the drives is 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 remaining drives. The general performance is also better as the reading and writing processes will be split between various drives, so a single one will never be overloaded. There are different kinds of RAIDs where the effectiveness and fault tolerance could differ based on the specific setup - whether information is written on all the drives real-time or it's written on a single drive and then mirrored on another, what number of drives are used for the RAID, and many others.