Template:Wikipedia Redundant Array of Independent Disks (RAID) is designed to prevent data loss in the event of a hard disk failure. There are different levels of RAID. RAID 0 (striping) is not really RAID at all, because it provides no redundancy. It does, however, provide a speed benefit. This example will utilize RAID 0 for swap, on the assumption that a desktop system is being used, where the speed increase is worth the possibility of system crash if one of your drives fails. On a server, a RAID 1 or RAID 5 array is more appropriate. The size of a RAID 0 array block device is the size of the smallest component partition times the number of component partitions.
RAID 1 is the most straightforward RAID level: straight mirroring. As with other RAID levels, it only makes sense if the partitions are on different physical disk drives. If one of those drives fails, the block device provided by the RAID array will continue to function as normal. The example will be using RAID 1 for everything except swap. Note that RAID 1 is the only option for the boot partition, because bootloaders (which read the boot partition) do not understand RAID, but a RAID 1 component partition can be read as a normal partition. The size of a RAID 1 array block device is the size of the smallest component partition.
RAID 5 requires 3 or more physical drives, and provides the redundancy of RAID 1 combined with the speed and size benefits of RAID 0. RAID 5 uses striping, like RAID 0, but also stores parity blocks distributed across each member disk. In the event of a failed disk, these parity blocks are used to reconstruct the data on a replacement disk. RAID 5 can withstand the loss of one member disk.
RAID does not provide a guarantee that your data is safe. If there is a fire, if your computer is stolen or if you have multiple hard drive failures, RAID will not protect your data. Therefore it is important to make backups. Whether you use tape drives, DVDs, CDROMs or another computer, keep an current copy of your data out of your computer (and preferably offsite). Get into the habit of making regular backups. You can also divide the data on your computer into current and archived directories. Then back up the current data frequently, and the archived data occasionally.