Following figure illustrates left-symmetric parity distribution. Each square corresponds to a stripe unit. Each column of squares corresponds to a disk. A useful property of the left-symmetric parity distribution is that whenever you traverse the striping units sequentially, you will access each disk once before accessing any disk device. This property reduces disk conflicts when servicing large requests.
Parity is a redundancy code capable of correcting any single, self-identifying failure.
As large disk arrays are considered, multiple failures are possible and stronger codes are needed. The probability of encountering an uncorrectable read error during recovery can be significant. Thus, applications with more stringent reliability requirements require stronger error correcting codes. Disks are mirrored in pairs for redundancy and improved performance, then data is striped across multiple disks for maximum performance. Obviously, RAID 10 uses more disk space to provide redundant data than RAID 5.