3Ware 3W-6800 - Escalade 6800 RAID Controller, Руководство пользователя

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3ware Escalade Storage Switch User Guide
10 www.3ware.com
RAID 5 arrays optimize performance, fault tolerance,
high capacity and storage efficiency
The RAID 5 configuration features the data striping of RAID 0
combined with the parity of RAID 4. Using a simple parity (exclu-
sive OR) function, RAID 5 can tolerate the loss of one drive. Parity
information is distributed across all drives rather than being con-
centrated on a single disk (see Figure 4). This avoids throughput
loss due to contention for the parity drive. You can use hot spares to
rebuild a failed drive “on-the-fly”.
RAID 5 capacity = size of smallest drive
×
(number of drives - 1).
In addition, the array’s storage efficiency increases with the number
of disks; from 66.7 % for 3 drives to 87.5 % for 8 drives: storage
efficiency = (number of drives -1)
÷
(number of drives).
Unlike all other RAID configurations that offer data striping, except
for RAID 1, RAID 5 stripe size is limited to 64k.
Note:
BIOS will reject the creation of a RAID 5 array
having less than 3 drives.
Figure 4. RAID 5 Configuration Example
RAID 5
A Blocks
0 parity
A4
A3
A2
A1
1 parity
B4
B3
B2 2 parity
C4
C3
C1
3 parity
D4
D2
D1
4 parity
E3
E2
E1
B0 C0 D0
E0
B Blocks C Blocks D Blocks
E Blocks