Raid 4 – HP StorageWorks 3000 RAID Array User Manual

Page 56

2-14 RAID Array 3000 Controller Shelf Hardware User’s Guide

Compaq Confidential – Need to Know Required

Writer: Bob Young Project: RAID Array 3000 Controller Shelf Hardware User’s Guide Comments:

Part Number: EK-SMCPQ-UG. D01 File Name: c-ch2 RAID Array 3000 Controller.doc Last Saved On: 12/4/00 1:08 PM

RAID 4

RAID 4 breaks up host data into chunks, calculates parity by performing 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 (Figure 2– 8). When the host
requests data from the disk drives, the controller retrieves the chunks
containing the addressed data, reconstitutes the data from the chunks, and
passes the data to the host.

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

0110

1011

0000

0110

1111

1110

Striped data and parity
written to the array

SHR-1057

0000

0111

XOr

Parity =

Figure 2-8. Diagram of a RAID 4 write