Allocating two different parities on different drives (double parity) makes it possible to recover from up to two
drive failures.
P2 M, N
, O, P
P2 I, J, K, L
A
E
I
M
A
B C D
Data writing request
B
F
J
P1 M, N, O, P
C
G
P1 I, J, K, L
D
P1 E, F, G, H P2 E, F
, G, H
N
K
O
P1
A, B, C, D
H
L
P
P2
A, B, C, D
A B DC
Create parity data
Drive#0 Drive#1 Drive#2 Drive#3 Drive#4 Drive#5
Parity for data A to D: P1 A, B, C, D and P2 A, B, C, D
Parity for data E to H: P1 E, F, G, H and P2 E, F, G, H
Parity for data I to L: P1 I, J, K, L and P2 I, J, K, L
Parity for data M to P: P1 M, N, O, P and P2 M, N, O, P
1. Function
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