HP A7143A RAID160 SA Controller Support Guide, February 2007

RAID Technology Overview

Smart Array Controller Supported RAID Configurations

Chapter 1

This fault-tolerance method is useful when high performance and data protection are more important than

the cost of physical disks.

The advantages of RAID 1+0 are as follows:

• Highest read and write performance of any fault-tolerant configuration.

• No loss of data as long as no of failed disks are mirrored to any other failed disk (up to half of the physical

disks in the array can fail).

The disadvantages of RAID 1+0 are as follows:

• Expensive — many disks are needed for fault tolerance.

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

RAID 5—Distributed Data Guarding

RAID 5 uses a parity data formula to create fault tolerance. In RAID 5, one block in each data stripe contains

parity data that is calculated for the other data blocks in that stripe. The blocks of parity data are distributed

over the physical disks that make up the logical drive, with each physical disk containing only one block of

parity data (see Figure 1-7). When a physical disk fails, the data that was on the failed disk can be calculated

from the parity data in the data blocks on the remaining physical disks in the logical drive. This recovered

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

RAID 5 is useful when cost, performance, and data availability are all equally important.

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

The advantages of RAID 5 are as follows:

• High read performance

• No loss of data if one physical disk fails.

• More usable disk drive capacity than with RAID 1+0; parity information only requires the storage space

equivalent to one physical disk on the array.

The disadvantages of RAID 5 are as follows:

• Relatively low write performance

• Data loss occurs if a second disk fails before data from the first failed disk is rebuilt.

P5,6

P3,4

P1,2

P7,8