RAID 3 is a striped RAID level designed to provide a performance increase by storing sequential bytes of data across multiple disks. Unlike RAID 0, which also provides a speed increase, RAID 3 supplements the speed increase with the use of a parity bit to improve data integrity.
Parity is calculated when data is written to the RAID 3 array; the parity data is stored on a dedicated separate disk. Because of the stored parity data, it's possible for a RAID 3 array made up of three or more disks to continue to operate without data loss, even if a single drive should fail. When a failed drive is replaced with a new one, the RAID 3 array can restore the missing data to the new disk.
RAID 3 storage size can be calculated by multiplying the smallest drive by the number of drives in the array, minus 1:
S = d * (n - 1)
"d" is the smallest disk in the array, and "n" is the number of disks that make up the array.
RAID 3 is usually used storing large files, such as multimedia, music, videos, and photos. Performance for writing or reading files larger than 1 MB is dramatically better than in a single-drive, non-RAID system; the same cannot be said for smaller, random file access. As such, RAID 3 may not be the best choice for a startup drive, but it makes an excellent choice for mass storage.