Appendix C RAID
17
(4) RAID6 Stripe 1
Stripe 3
Parity 1 (5, 6)
Parity 2 (N, N+1)
Stripe 2
Stripe N
Parity 1 (3, 4)
Stripe 5
Stripe N+1
Parity 1 (1, 2)
Parity 2 (5, 6)
Parity 2 (3, 4)
Parity 2 (1, 2)
Stripe 4
Stripe 1 Stripe 2 Stripe 3 Stripe 4 Stripe 5 Stripe 6 Stripe N ...
Parity 2 Generation
Parity 1 Generation
Data Sent from Host
Physical Disk 1 2 3 4
Stripe 6
Parity 1 (N, N+1)
Striping Size
This method slices data sent from the host in certain striping size and distributes the slices into the
physical disks of the RAID. While doing that, it generates two parity data per block and
distributes the respective parities into the disks.
RAID6 supports double parity, therefore it secures redundancy even if one disk becomes faulty
and also ensures accessibility even if two disks become faulty. However, the capability for
reading data degrades in case of a disk failure.
In addition to that, RAID6 distributes parity data to multiple disks, it enables concurrent
processing for access to the disks. Thus, RAID6 is suitable for random access to small files in
size of several kilobytes.
<Advantage>
y Redundancy secured if one physical disk becomes faulty, and high reliability and availability if
two disks become faulty.
y Concurrent processing by using distributed parities
y Suitable for random access
<Disadvantage>
y If two physical disks used for the logical disks fail, the capability for reading data degrades.