Fujitsu Eternus DX60 User Manual page 27

Chapter 1 Overview
> 1.2 Configuration
• RAID6 (striping with distributed double parities)
Store two different parities on different disks (double parities) to recover from up to two disk
failures.
Figure 1.6
User capacity for each RAID level
User capacity varies according to the RAID level.
Table 1.1
Table 1.1
RAID level
RAID0
RAID1
RAID1+0
RAID5
RAID5+0
RAID6
*1: Actual number of disks can be installed depend on the models.
P3AM-3042-03ENZ0 ETERNUS DX60/DX80 Disk storage system User Guide
Data writing request
A B C
A B C
A B C
E F G
I J P1
I, J, K, L
M P1 P2
M, N, O, P M, N, O, P
HDD0 HDD1 HDD2
Parity for data A to D: Parity1
Parity for data E to H: Parity1
Parity for data I to L:
Parity for data M to P: Parity1
RAID6 Concept
shows the formula for user capacity computation.
User Capacity for each RAID Level
Number of disks (*1)
2 to 16
2
4 to 32
3 to 16
6 to 32
5 to 16
D
D Create parity data
P1 P2
A, B, C, D
D
P1 P2
E, F, G, H E, F, G, H
P2
I, J, K, L K
N O
HDD3 HDD4
and Parity2
A, B, C, D
E, F, G, H and Parity2
Parity1 I, J, K, L and Parity2
and Parity2
M, N, O, P
Formula for user capacity computation
Disk capacity × Number of disks
Disk capacity × Number of disks/2
Disk capacity × Number of disks/2
Disk capacity ×
(Number of disks - 1)
Disk capacity ×
(Number of disks - 2)
Disk capacity ×
(Number of disks - 2)
27
A, B, C, D
H
L
P
HDD5
A, B, C, D
E, F, G, H
I, J, K, L
M, N, O, P
Copyright 2009 FUJITSU LIMITED