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Chapter 2. RAID Array Controller
EK–SMCPQ–UG. C01 2–13
2.6.4 RAID 4
RAID 4 (Figure 2–8) breaks up host data into chunks, calculates parity by per-
forming an exclusive-or on the chunks, and then writes the chunks to all but one
drive in the array and the parity data to the last drive. When the host requests
data from the disk drives, the controller retrieves the chunks containing the ad-
dressed data, reconstitutes the data from the chunks, and passes the data to the
host.
Figure 2–8 Diagram of a RAID 4 Write
0011
1011
0110
1110
0110
0000
1111
1110
Host Data
Controller divides the
data into chunksized units
and calculates parity
There is still data left
so the Controller
repeats the Process
0011
0011
0110
0110
1011
1011
0000
0000
0110
0110
1111
1111
1110
1110
1110
1110
Striped data and parity
written to the array
Striped data and parity
written to the array
S
HR-1
0
5
7
0000
0111
XOr
XOr
Parity =
Parity =