Raid 4; Diagram Of A Raid 4 Write - Compaq StorageWorks RAID Array 3000 Controller Shelf Hardware User's Manual

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
Host Data
0011 0110
1011 0000
0110 1111
1110 1110
EK–SMCPQ–UG. C01
Controller divides the
data into chunksized units
and calculates parity
0011 0110
Striped data and parity
1011 0000
written to the array
0110 1111
XOr 1110 1110
Parity =
0000
There is still data left
so the Controller
repeats the Process
0011 0110
Striped data and parity
1011 0000
written to the array
0110 1111
XOr 1110 1110
Parity =
0111
Chapter 2. RAID Array Controller
SHR-1057
2–13