Redundant Array of Independent Disks, or RAID, is a method of saving content on a number of hard disks concurrently. A RAID can be software or hardware depending on the HDDs that are used - physical or logical ones, however what is common between them is that they all function as a single unit where information is saved. The key advantage of employing a RAID is redundancy because the data on all the drives is identical all the time, so even in case some drive fails for whatever reason, the info will still be available on the remaining drives. The general performance is also enhanced since the reading and writing processes will be split between multiple drives, so a single one won't be overloaded. There are different types of RAIDs where the effectiveness and fault tolerance can vary depending on the exact setup - whether information is written on all drives in real time or it is written on one drive and then mirrored on another, the number of drives are used for the RAID, and so on.