Redundant Array of Independent Disks, or RAID, is a way of saving content on a number of hard disk drives simultaneously. A RAID might be software or hardware based on the hard drives which are used - physical or logical ones, however what’s common between them is that they all work as a single unit where info is saved. The biggest advantage of using a RAID is redundancy because the data on all of the drives will be the same at all times, so even in case one of the drives fails for whatever reason, the data will still be present on the rest of the drives. The general performance is enhanced as well since the reading and writing processes could be split between multiple drives, so a single one won't be overloaded. There are different types of RAIDs where the functionality and fault tolerance can vary according to the exact setup - whether data is written on all the drives real-time or it is written on one drive and afterwards mirrored on another, the number of drives are used for the RAID, etc.