HP A7143A RAID160 SA Controller Support Guide

RAID Technology Overview

HP RAID160 SA Controller Supported RAID Configurations

Chapter 122

Disadvantages

• Expensive (many disks needed for fault tolerance)

• Only 50% of total disk drive capacity usable for data storage

RAID 5—Distributed Data Guarding

RAID 5 employs a parity data formula. With this configuration, one block

in each data stripe contains parity data that is calculated for each data

block in that stripe. The blocks of parity data are distributed over the

physical disks that make up the logical drive, with each physical disk

having only one block of parity data (see Figure 1-7, “Distributed Data

Guarding, Showing Parity Information (Px,y),”). When a physical disk

fails, the data that was on the failed disk can be calculated from the data

blocks on the remaining physical disks in the logical drive, by using the

parity data for each stripe in that logical drive. This recovered data is

usually written to an online spare in a process called a rebuild.

This configuration is useful when cost, performance, and data

availability are equally important.

Figure 1-7 Distributed Data Guarding, Showing Parity Information (Px,y)

Advantages

• High read performance

• No loss of data if one physical disk fails

P5,6

P3,4

P1,2

P7,8