Symmetrix DMX RAID 5
199
Data Integrity, Availability, and Protection
Figure 43 RAID 5 data/parity (3+1)
RAID 5 (3+1)
A RAID 5 (3+1) configuration consists of four Symmetrix devices
with parity and data striped across each device. With this option,
effectively 75 percent of the total storage capacity of a RAID 5 device
is available for storing data.
RAID 5 (7+1)
A RAID 5 (7+1) configuration consists of eight Symmetrix devices
with data and parity striped across each device. With this option,
effectively 87.5 percent of total storage capacity of each RAID 5
device is available for storing data.
RAID 5 modes of
operation
RAID 5 has the following modes of operation:
◆ “Normal mode” on page 199
◆ “Regeneration” on page 200
◆ “Fast Copy Back” on page 200
Normal mode When a RAID 5 device operates with all hypervolumes functioning, it
is operating in normal mode. In normal mode, the Symmetrix DMX
system accomplishes data redundancy by using the standard
EXCLUSIVE OR (XOR) logic to generate and store parity that can
then be used to reconstruct the information stored on a failed/failing
member.
SYM-000547
LV D
1
LV B
1
LV C
1
Parity 123
Data 4
Data 7
Parity DEF
Data G
Data J
Data M
2
LV D
2
LV C
2
LV B
Data 1
Parity 456
Data 8
Data D
Parity GHI
Data K
Data N
LV D
3
LV C
3
LV B
3
Parity 789
Parity JKL
Data 2
Data 5
Data E
Data H
Data O
LV D
4
LV C
4
LV B
4
Data 3
Data 6
Data 9
Data F
Data I
Data L
Parity MNO...
Physical
disk 1
Physical
disk 2
Physical
disk 3
Physical
disk 4
RAID 5
logical
volume
A
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