A RAID array connects two or more hard drives together to make what is essentially a single giant hard drive. RAID arrays offer greater storage capacity, protection against data loss from individual drive failure, increased efficiency, or some combination of the three.
A RAID-5 is a redundant array of independent disks which splits all of the data written to it and “stripes” it across all of the drives in the array. A single block of data in a RAID array is typically 128 sectors on a hard disk drive, or 64 kilobytes. Unlike RAID-0, which also uses this striping technique to link its drives together, a RAID-5 array also has “parity” blocks.
These special blocks hold bits of parity data so that if any single drive in the array fails, the RAID controller can use XOR logic to piece together the missing data. This parity data takes up a total of one drive’s worth of space in the array, regardless of how many drives are in the array. A RAID-5 array has one less drive’s worth of storage capacity than a RAID-0 with the same amount of equally-sized drives. However, multiple drive failures can still cause RAID 5 data loss.