Alternatively, you can use a spare hard drive that is removable and can be taken off-site. A set of RAID drives comes with a special hard drive controller with RAID functionality built into it. This allows several disk drives do the task of one drive and improves the speed. Mirroring is the practice of creating and maintaining an exact replica of the original data and is usually updated frequently to ensure that it reflects the content of the original data. However, it is also the most expensive method, because it doubles disk storage space requirements.
Parity uses a bit-level calculation to combine the data in two drives into a third drive.
RAID 1 consists of two hard disks, one of which mirrors the data on the other. If the disk fails, your data is instantly available on the mirroring disk, without any rebuild time. Because RAID 1 requires you to buy twice as many drives as you need for data, it may be too expensive for most small businesses. It consists of three or more disks and provides performance gains through striping and fault protection through parity. With RAID 5, one disk out of the set of three or more can fail and the system will be able to automatically rebuild the data.