RAID layouts

RAID layouts

mdadm supports not only multiple levels of RAID (0, 1, 10, 5, 6) but also different layouts of the particular levels. Below is a description of some of them.

RAID 6

RAID 6 left-symmetric (level 6, algorithm 2)

RAID 6 uses 2 chunks to keep parity data of the data chunks. One chunk is calculated using XOR and the other using Reed-Solomon algorithm

Disk 0	Disk 1	Disk 2	Disk 3
Q[12P]	1	2	P[12]
3	4	P[34]	Q[34P]
6	P[56]	Q[56P]	5
P[78]	Q[78P]	7	8

Where P[xy] is the XOR parity over block x and y while Q[xyz] is Reed-Solomon parity over block x, y and z

Conversely, for 6-disk array:

Disk 0	Disk 1	Disk 2	Disk 3	Disk 4	Disk 5
Q	1	2	3	4	P
5	6	7	8	P	Q
10	11	12	P	Q	9
15	16	P	Q	13	14
20	P	Q	17	18	19
P	Q	21	22	23	24
Q	25	26	27	28	P
29	30	31	32	P	Q
34	35	36	P	Q	33