Redundant Array of Independent Disks, or RAID, is a method of storing content on multiple hard disk drives concurrently. A RAID could be software or hardware based on the HDDs that are used - physical or logical ones, but what’s common between them is that they all work as a single unit where your information is saved. The main advantage of using a RAID is redundancy as the info on all the drives shall be exactly the same at all times, so even in the event that one of the drives fails for some reason, the information will still be available on the remaining drives. The general performance is enhanced as well because the reading and writing processes can be split between different drives, so a single one won't be overloaded. There are different kinds of RAIDs where the effectiveness and fault tolerance may vary depending on the specific setup - whether data is written on all the drives real-time or it's written on one drive and then mirrored on another, the number of drives are used for the RAID, and so on.