Redundant Array of Independent Disks, or RAID, is a way of keeping content on a number of hard drives at the same time. A RAID might be software or hardware based on the hard drives that are used - physical or logical ones, yet what is common between them is the fact that they all function as just one single unit where information is saved. The biggest advantage of employing a RAID is redundancy because the data on all drives shall be exactly the same all the time, 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 also better since the reading and writing processes will be split between multiple drives, so a single one can't be overloaded. There're different kinds of RAIDs where the capabilities and fault tolerance could differ based on the exact setup - whether data is written on all drives in real time or it's written on one drive and then mirrored on another, what number of drives are used for the RAID, and many others.