Compaq 3000 manual Diagram of a RAID 4 Write

Chapter 2. RAID Array Controller

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		Controller divides the
		data into chunksized units
0011	0110	and calculates parity
1011	0000		0011	0110	Striped data and parity
0110	1111		1011	0000
					written to the array
1110	1110		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

SHR-1057

EK–SMCPQ–UG. C01 2–13