3Ware 3W-6800 User Guide - Page 20

RAID 5 arrays optimize performance, fault tolerance, high capacity and storage efficiency, - bios

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3ware Escalade Storage Switch User Guide 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 (exclusive OR) function, RAID 5 can tolerate the loss of one drive. Parity information is distributed across all drives rather than being concentrated 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. RAID 5 0 parity A1 A2 A3 A4 A Blocks B0 1 parity B2 B3 B4 B Blocks C0 C1 2 parity C3 C4 C Blocks D0 D1 D2 3 parity D4 D Blocks E0 E1 E2 E3 4 parity E Blocks Figure 4. RAID 5 Configuration Example 10 www.3ware.com

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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