IBM Netfinity ServeRAID-3H User manual

IBM
IBM Netfinity
ServeRAID-3H, ServeRAID-3HB, and ServeRAID-3L
Ultra2 SCSI Controllers
Installation and User's Guide

IBM IBM Netfinity
ServeRAID-3H, ServeRAID-3HB, and ServeRAID-3L
Ultra2 SCSI Controllers
Installation and User's Guide

Note
Before using this information and the product it supports, be sure to read the general information under
Appendix A, “Product warranties and notices” on page 157.
Second Edition (June 1999)
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 Copyright International Business Machines Corporation 1996, 1999. All rights reserved.
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Contents
About this book .................................................. vii
How this book is organized ............................................ vii
Notices used in this book ............................................. viii
Chapter 1. Getting started . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Option package contents ............................................. 2
Installation overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Understanding RAID technology ......................................... 4
Stripe-Unit size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Supported RAID levels ............................................. 5
Chapter 2. Installing and cabling a ServeRAID controller ........................ 13
Controller features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Connector locations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Installing the ServeRAID controller ........................................ 17
Connecting external devices ........................................... 18
Chapter 3. Using the configuration programs ............................... 19
Using the ServeRAID Configuration Program .................................. 20
Starting the Configuration Program ...................................... 21
Using the Configuration Mode ......................................... 22
Using the Information Mode .......................................... 26
Changing the ServeRAID configuration settings .............................. 31
Using the Tool Bar ............................................... 31
Using the Menu Bar ............................................... 32
Configuring two ServeRAID 3 controllers in a failover environment (Windows NT 4.0 Only) ....... 37
Hardware requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
Installation guidelines, considerations, and restrictions ........................... 38
Configuring the controllers in a failover environment ............................ 39
Configuring the controllers for failover .................................... 40
Connecting the expansion enclosures .................................... 41
Configuring logical drives ............................................ 41
Setting Merge Group Numbers ........................................ 42
Using the ServeRAID Mini-Configuration Program ............................... 44
Viewing the controller status .......................................... 44
Viewing the configuration ............................................ 45
Using the Advanced Configuration functions ................................ 45
Chapter 4. Installing device drivers and utility programs ........................ 47
IBM ServeRAID Configuration and Management CD and diskettes ..................... 49
ServeRAID Manager Program .......................................... 50
Installing the ServeRAID Manager program for Windows NT ....................... 50
Installing the ServeRAID Manager Program for UnixWare ........................ 50
Administration and Monitoring Program ..................................... 51
Programs for Windows NT and Windows 95 ................................ 51
Background-Server components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
Programs for OS/2 and NetWare ....................................... 52
Programs for OpenServer and UnixWare .................................. 52
Installing the ServeRAID WIN32-Based program ............................... 53
Installing ServeRAID device drivers ....................................... 53
 Copyright IBM Corp. 1996, 1999 iii

Installing device drivers for Windows NT ................................... 54
Installing the files for Windows NT 3.5 .................................... 54
Installing the files for Windows NT 3.5 .................................... 54
Installing the files for Windows NT 4.0 .................................... 56
Installing device drivers for NetWare ..................................... 58
Installing device drivers for OS/2 ....................................... 61
Installing device drivers for OpenServer ................................... 64
Installing device drivers for UnixWare .................................... 67
Starting the Background-Server components ................................ 70
Using the Background-Server components ................................. 71
IBM ServeRAID fault-tolerant applet ....................................... 73
Using the applet screen ............................................ 73
Command-Line Programs - IPSSEND and IPSMON ............................. 74
Installing IPSSEND and IPSMON for OS/2, NetWare, or Windows NT ................. 74
Installing IPSSEND and IPSMON for OpenServer ............................. 75
Installing IPSSEND and IPSMON for UnixWare .............................. 76
Installing IPSSEND for IBM DOS ....................................... 76
Chapter 5. The ServeRAID Manager program ............................... 79
Using the ServeRAID Manager program .................................... 80
Starting the ServeRAID Manager Program ................................. 81
Using the Information Mode .......................................... 83
Changing the ServeRAID configuration settings .............................. 88
Using the Tool Bar ............................................... 89
Using the Menu Bar ............................................... 89
Using the Configuration Mode ......................................... 93
Logical Drive Migration ............................................. 93
Notification Manager . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
Notification Manager Screen .......................................... 94
Using the Tool Bar ............................................... 95
Understanding the Notification List ...................................... 95
Understanding the Notification Event Viewer and events ......................... 96
Security Manager . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
Security Manager Screen ........................................... 97
Using the Tool Bar ............................................... 98
Understanding the Security List ........................................ 98
Understanding the Security Event Viewer and events ........................... 98
Chapter 6. Starting and using the Administration and Monitoring Program ............ 101
Starting and Using the Administration and Monitoring Program ...................... 102
Using the Administration and Monitoring Program .............................. 103
Using the Options Pull-Down Menu ..................................... 103
Using the administration functions ..................................... 107
Using the monitoring functions ....................................... 117
Chapter 7. Starting and using the command line programs ..................... 121
Starting the IPSSEND program ......................................... 122
Using the IPSSEND program .......................................... 122
Server Roll-Out commands ......................................... 122
Error-Recovery commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124
Problem-Isolation and Debug commands ................................. 125
RAID Configuration commands ....................................... 128
FLASHCOPY commands (for Windows NT only) ............................. 129
Starting the IPSMON program ......................................... 134
iv IBM ServeRAID-3H, ServeRAID-3HB, and ServeRAID-3L, Controllers

Using the IPSMON program .......................................... 135
Chapter 8. Solving ServeRAID problems ................................. 137
ServeRAID controller messages ........................................ 138
ServeRAID startup messages ........................................ 138
ServeRAID POST messages ........................................ 142
ServeRAID ISPR, BCS, and ECS codes .................................. 142
Rebuilding a defunct drive ............................................ 147
Steps for recovering from defunct (DDD) drives ............................. 147
Rebuilding a hot-swap drive ......................................... 147
Troubleshooting an incomplete format of a hard disk drive ......................... 148
Troubleshooting a failure in a failover-environment ............................. 148
Replacing a non-hot-plug controller in a failover pair ........................... 149
Chapter 9. Getting help, service, and information ............................ 151
Before you call for service ............................................ 151
Getting customer support and service ..................................... 152
Using electronic support services ...................................... 152
Using the World Wide Web ......................................... 152
Getting information by fax .......................................... 153
Getting help online .............................................. 153
Getting help by telephone .......................................... 153
Getting help around the world ........................................ 154
Purchasing additional services ......................................... 155
900-Number operating system and hardware support line ........................ 155
Network and server support line ...................................... 155
Ordering support line services ........................................ 155
Warranty and repair services ........................................ 156
Ordering publications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156
Appendix A. Product warranties and notices .............................. 157
Warranty Statements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157
IBM Statement of Limited Warranty for United States, Puerto Rico, and Canada (Part 1 - General
Terms) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157
IBM Statement of Warranty Worldwide except Canada, Puerto Rico, Turkey, United States (Part 1
- General Terms) .............................................. 159
Part 2 - Worldwide Country-Unique Terms ................................ 161
Notices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164
Year 2000 readiness and instructions ................................... 164
Trademarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164
United Kingdom telecommunications safety requirement ........................ 166
European community directive conformance statement ......................... 166
Industry Canada Class A Emission Compliance Statement ....................... 166
Australia and New Zealand Class A Statement .............................. 166
Taiwanese electromagnetic interference (EMI) statement ........................ 167
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169
Contents v

vi IBM ServeRAID-3H, ServeRAID-3HB, and ServeRAID-3L, Controllers

About this book
This book provides the information needed to install and configure an IBM Netfinity ServeRAID-3H
Ultra2 SCSI Controller, an IBM ServeRAID-3HB Ultra2 SCSI Controller, or an IBM ServeRAID-3L Ultra2
SCSI Controller. You also can use the configuration and reference information in this book to configure
the IBM ServeRAID controllers provided on some IBM Netfinity and PC Server system boards.
Note: The IBM ServeRAID product can be either a controller built-in on an adapter card, such as the one
in this option package, or a controller that is built-in on the system board of your server. For
purposes of consistency in this manual, we will refer to the ServeRAID product as a ServeRAID
controller, unless it is specifically noted otherwise.
How this book is organized
Chapter 1, “Getting started,” contains introductory information about the IBM ServeRAID-3H and
ServeRAID-3L controllers, a content listing for the ServeRAID option package, an installation overview,
and general information about RAID technology.
Chapter 2, “Installing and cabling a ServeRAID controller,” provides information about the standard
features of the ServeRAID-3H and ServeRAID-3L controllers, and instructions for installing and cabling a
ServeRAID controller that is on an adapter.
Chapter 3, “Using the configuration programs,” explains how to use the IBM ServeRAID Configuration
Program and the IBM ServeRAID Mini-Configuration Program. You can refer to the information in this
chapter when configuring one or more devices attached to a ServeRAID controller.
Chapter 4, “Installing device drivers and utility programs,” contains the instructions needed to install the
ServeRAID device drivers and programs provided on the IBM ServeRAID Configuration and Management
CD and diskettes that came with the ServeRAID controllers.
Chapter 5, “The ServeRAID Manager program,” contains the instructions for using the ServeRAID
Manager program under Microsoft Windows 95, Windows 98, Windows NT, or UnixWare.
Chapter 6, “Starting and using the Administration and Monitoring Program,” contains instructions for
starting and using the ServeRAID Administration and Monitoring Program. You can use these
operating-system specific programs to maintain and monitor your ServeRAID subsystem.
Chapter 7, “Starting and using the command line programs,” contains instructions for starting and using
the IPSSEND and IPSMON command line programs. You can use these operating-system specific
programs to maintain and monitor your ServeRAID subsystem.
Chapter 8, “Solving ServeRAID problems,” describes the ServeRAID POST error codes and startup
messages. This chapter also includes some basic information about rebuilding a defunct drive.
Chapter 9, “Getting help, service, and information,” provides information about accessing the IBM Bulletin
Boards, HelpCenter, and World Wide Web sites to obtain future code and information updates for the
ServeRAID controllers.
Appendix A, “Product warranties and notices,” contains warranty information, product notices, and
trademarks.
 Copyright IBM Corp. 1996, 1999 vii

Notices used in this book
This book contains notices to highlight information as follows:
Notes:
These notices provide important tips, guidance, or advice.
Attention:
These notices indicate possible damage to programs, devices, or data. An attention notice is placed
just before the instruction or situation in which damage could occur.
viii IBM ServeRAID-3H, ServeRAID-3HB, and ServeRAID-3L, Controllers

Chapter 1. Getting started
This book provides the information needed to install and configure an IBM ServeRAID-3H Ultra2 SCSI
Controller, an IBM ServeRAID-3L Ultra2 SCSI Controller, or an IBM clarhb.. These high-performance,
redundant array of independent disk (RAID) controllers are ideally suited for data-storage environments
that require superior performance, flexibility, and reliable data storage. (See “Controller features” on
page 14 for more information.)
You also can use the configuration and reference information in this book to configure the IBM ServeRAID
controllers provided on some IBM Netfinity and PC Server system boards.
This chapter contains:
Option package contents ............................................. 2
Installation overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Understanding RAID technology ......................................... 4
Stripe-Unit size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Supported RAID levels ............................................. 5
Understanding RAID level-0 ........................................ 5
Understanding RAID Level-1 ........................................ 7
Understanding Enhanced RAID Level-1 ................................. 8
Understanding RAID Level-5 ........................................ 9
Understanding Enhanced RAID Level-5 ................................. 11
Selecting a RAID level and performance turning ............................ 12
 Copyright IBM Corp. 1996, 1999 1

Option package contents
In addition to this book, the ServeRAID option package contains:
IBM Netfinity ServeRAID-3L Ultra2 SCSI Controller or
IBM Netfinity ServeRAID-3H Ultra2 SCSI Controller or
IBM Netfinity ServeRAID-3HB Ultra2 SCSI Controller with battery-backup write cache.
Attention:
Do not open the static-protective bag containing the controller until you are instructed to do so.
IBM ServeRAID Support Package:
– IBM ServeRAID Configuration and Management CD
– IBM ServeRAID Device Driver Diskette
– IBM Netfinity Device Drivers for SCO Operating Systems Diskette
See Chapter 4, “Installing device drivers and utility programs” on page 47 for more detailed
information.
IBM ServeRAID Channel 3 Cable option kit
This cable comes with the ServeRAID-3H controller and the ServeRAID-3HB controller only. You can
attach this cable to the ServeRAID-3H controller or the ServeRAID-3HB controller to convert the
internal SCSI channel connector to an external connector. See “ServeRAID-3H and ServeRAID-3HB
controller” on page 15 for more information.
Contact your place of purchase if any items are missing or damaged.
2IBM ServeRAID-3H, ServeRAID-3HB, and ServeRAID-3L, Controllers

Installation overview
This book contains reference, installation, configuration, and administration information for the IBM
ServeRAID-3H controller, ServeRAID-3L controller, and ServeRAID controllers. In addition to this book,
you might need to refer to your IBM server documentation for Safety information, connector locations, and
for controller and hard disk drive installation instructions.
Note: The IBM ServeRAID product can be either a controller built-in on an adapter card, such as the one
in this option package, or a controller that is built-in on the system board of your server. For
purposes of consistency in this manual, we will refer to the ServeRAID product as a ServeRAID
controller, unless it is specifically noted otherwise.
The information that you will need to install or configure your IBM ServeRAID subsystem depends on the
type of ServeRAID controller you are using and your familiarity with RAID technology.
A typical installation and configuration of an IBM ServeRAID subsystem consists of the following steps:
1Learn about RAID technology.
The “Understanding RAID technology” section in this chapter contains general information about
RAID technology. If you already are familiar with the IBM implementation of RAID technology, you
might want to start your installation with step 2.
2Install the ServeRAID-3H or ServeRAID-3L Controller.
Chapter 2, “Installing and cabling a ServeRAID controller” provides information about the standard
features of the ServeRAID-3H and ServeRAID-3L controllers, and installation and cabling instructions
for the controllers. You will not need the information in this chapter if you are using a ServeRAID
controller on an IBM Netfinity or PC Server system board.
3Use the ServeRAID Configuration Programs to configure your disk arrays.
Chapter 3, “Using the configuration programs” explains how to use the IBM ServeRAID
Configuration Program and the IBM ServeRAID Mini-Configuration Program. You can refer to the
information in this chapter or the online information in the configuration program when configuring
one or more devices attached to a ServeRAID controller.
Attention:
The default setting for the stripe-unit size is 8 KB1. If you want to use a different setting, be sure to
change the stripe-unit size before you store data in the logical drives. After you store data in the
drives, you cannot change the stripe-unit size without destroying data in the logical drives. (See
“Stripe-Unit size” on page 4 and page 34 for more information.)
If you are configuring a ServeRAID-3H Ultra2 SCSI Controller or a ServeRAID-3L Ultra2 SCSI
Controller, see Chapter 3, “Using the configuration programs” on page 19 for instructions.
If you are configuring an IBM ServeRAID controller that came as a standard feature on an IBM
Netfinity or PC Server system board, see the installation instructions and CDs provided with your
server for information about starting the configuration programs for the server.
4Install your operating system, ServeRAID device drivers, and ServeRAID utility programs.
You can skip this step if you are installing multiple ServeRAID controllers and you already installed
your operating system and the most current versions of the ServeRAID device drivers and utility
programs.
1KB equals approximately 1000 bytes.
Chapter 1. Getting started 3

To install these files for a ServeRAID-3H Ultra2 SCSI Controller or a ServeRAID-3L Ultra2 SCSI
Controller, see the information provided with your operating system and Chapter 4, “Installing
device drivers and utility programs” on page 47 for instructions.
To install these files for an IBM ServeRAID controller that came as a standard feature on an IBM
Netfinity or PC Server system board, see the installation instructions and CDs provided with your
server for instructions.
After you install the device drivers, refer to one of the following chapters.
If you are using Windows NT or UnixWare, refer to Chapter 5, “The ServeRAID Manager
program” on page 79.
If you are using any other operating system, refer to Chapter 6, “Starting and using the
Administration and Monitoring Program” on page 101.
If you want to use the command line programs, refer to Chapter 6, “Starting and using the
Administration and Monitoring Program” on page 101.
Understanding RAID technology
RAID is the technology of grouping several hard disk drives in a computer into an array that you can
define as one or more logical drives. Each logical drive appears to the operating system as a single drive.
This grouping technique greatly enhances logical-drive capacity and performance beyond the physical
limitations of a single hard disk drive.
When you group multiple physical hard disk drives into a logical drive, the ServeRAID controller can
transfer data in parallel from the multiple drives in the array. This parallel transfer yields data-transfer
rates that are many times higher than with nonarrayed drives. This increased speed makes the system
better able to meet the throughput (the amount of work in a given amount of time) or productivity needs of
the multiple-user network environment.
The ability to respond to multiple data requests provides not only an impressive increase in throughput,
but also a decrease in response time. The combination of parallel transfers and simultaneous responses
to multiple requests allows disk arrays to provide a high level of performance in network environments.
Stripe-Unit size
With RAID technology, data is striped across an array of hard disk drives. This data-distribution scheme
complements the way the operating system requests data.
The granularity at which data from one file is stored on one drive of the array before subsequent data is
stored on the next drive of the array is called the stripe-unit size.
You can control the stripe-unit size and maximize the performance of your ServeRAID controller by setting
a stripe-unit size to a value that is close to the size of the system I/O requests. You can set the stripe-unit
size to 8 KB, 16 KB, 32 KB, or 64 KB. For example, performance in transaction-based environments,
which typically involve large blocks of data, might be optimal when the stripe-unit size is set to 32 KB or
64 KB; however, performance in file and print environments, which typically involve multiple small blocks
of data, might be optimal when the stripe-unit size is set to 8 KB or 16 KB.
The collection, in logical order of these stripe units, from the first drive of the array to the last drive of the
array, is called a stripe.
Note: Eight physical drives are supported in an array if the stripe-unit size is set to 32 KB or 64 KB.
Sixteen physical drives are supported in an array if the stripe-unit size is set to 8 KB or 16 KB.
4IBM ServeRAID-3H, ServeRAID-3HB, and ServeRAID-3L, Controllers

Supported RAID levels
Disk arrays are used to improve performance and reliability. The amount of improvement depends on the
application programs that you run on the server and the RAID levels that you assign to the logical drives.
The ServeRAID controllers support RAID level-0, RAID level-1, Enhanced RAID level-1 (1E), RAID level-5
and Enhanced RAID level-5 (5E).
Understanding RAID level-0
RAID level-0 stripes the data across all the drives in the array. This offers substantial speed
enhancement, but provides for no data redundancy. RAID level-0 provides the largest capacity of the
RAID levels offered, because no room is taken up for redundant data or data-parity storage.
RAID level-0 requires a minimum of one drive and, depending upon the stripe-unit size, supports a
maximum of eight or 16 drives.
The following illustration shows an example of a RAID level-0 logical drive.
You start with two physical drives.
Create an array using the two physical drives.
Then, create a logical drive within that array.
The firmware stripes data across the drives, creating
blocks.
Notice that the data is striped across all of the drives in
the array, but no redundant data is stored. 1 2
3 4
5 6
7 8
Chapter 1. Getting started 5

A hard disk drive failure within the array results in loss of data in the logical drive assigned RAID level-0,
but only in that logical drive. If you have logical drives in the same array assigned to other RAID levels (1,
1E, 5, or 5E), they will not lose any data.
Note: If your array contains one physical drive, you only can assign RAID level-0.
When you replace a failed drive, the ServeRAID controller rebuilds all of the RAID level-1 and RAID
level-5 logical drives automatically onto the replacement hard disk drive. However, any data stored in a
failed RAID level-0 logical drive is lost.
Though the risk of data loss is present, you might want to assign RAID level-0 to one of the logical drives
to take advantage of the speed offered with this RAID level. You could use this logical drive to enter data
that you back up each day and for which safety is not of primary importance, such as data that you can
easily re-create. You also might want to use a RAID level-0 logical drive when the work you are doing
requires maximum capacity.
6IBM ServeRAID-3H, ServeRAID-3HB, and ServeRAID-3L, Controllers

Understanding RAID Level-1
RAID level-1 provides 100% data redundancy and requires only two hard disk drives. With RAID level-1,
the first half of a stripe is the original data, and the second half of a stripe is a mirror (copy) of the data,
but written to the other drive in the RAID level-1 array.
Because the data is mirrored, the capacity of the logical drive when assigned RAID level-1 is 50% of the
array capacity.
The following illustration shows an example of a RAID level-1 logical drive.
You start with two physical drives.
Create an array using the two physical drives.
Then, create a logical drive within that array.
The firmware stripes data across the drives, creating
blocks.
Notice that the data on the drive on the right is a mirror
copy of the drive on the left. 1 1
2 2
3 3
4 4
If one of the hard disk drives fails in this example, the ServeRAID controller switches read and write
requests to the remaining functional drive in the RAID level-1 array.
Chapter 1. Getting started 7

Understanding Enhanced RAID Level-1
If you have three or more hard disk drives in the array, you can no longer select RAID level-1, but you can
select Enhanced RAID level-1 (also called RAID level-1E).
RAID level-1E combines mirroring with data striping. This RAID level stripes data and copies of the data
across all of the drives in the array. As with the standard RAID level-1, the data is mirrored, and the
capacity of the logical drive is 50% of the array capacity.
RAID level-1E requires a minimum of three drives and, depending upon the stripe-unit size, supports a
maximum of eight or 16 drives.
The following illustration is an example of an Enhanced RAID level-1 logical drive.
You start with three physical drives.
Create an array using the physical drives.
Then, create a logical drive within that array.
The firmware stripes data across the drives, creating
blocks.
Notice that the stripe labeled with * is the data stripe
and the stripe labeled with * * is the mirror, or copy, of
the preceding data stripe. Also notice that each block on
the mirror stripe is shifted one drive.
1 2 3
3 1 2
4 5 6
6 4 5
x*
*
*
*
*
*
If one of the hard disk drives fails in this example, the ServeRAID controller switches read and write
requests to the remaining functional drives in the RAID level-1E array.
8IBM ServeRAID-3H, ServeRAID-3HB, and ServeRAID-3L, Controllers

Understanding RAID Level-5
RAID level-5 requires a minimum of three hard disk drives. This RAID level stripes data and parity across
all drives in the array. When an array is assigned RAID level-5, the capacity of the array is reduced by
one drive (for data-parity storage).
RAID level-5 is generally the most desirable choice, because it offers both data protection and increased
throughput. RAID level-5 gives you higher capacity than RAID level-1, but RAID level-1 offers better
performance.
The RAID level-5 requires a minimum of three drives and, depending upon the stripe-unit size, supports a
maximum of eight or 16 drives.
The following illustration is an example of a RAID level-5 logical drive.
You start with four physical drives.
x
Create an array using three of the physical drives and
leaving the fourth as a hot-spare.
x
Then, create a logical drive within that array.
x
The firmware stripes data across the drives, creating
blocks.
Notice that the storage of the data parity (denoted by * )
also is striped, and it shifts from drive to drive.
A parity block (denoted by *) is calculated from the data
on other blocks in the same stripe.
x*
**
3 4
1 2
*
5 6
7 8
Chapter 1. Getting started 9

If a hard disk drive fails in the array in this example, the
ServeRAID controller switches read and write requests to
the remaining functional drives in the RAID level-5 array
until the hot-spare finishes rebuilding.
x**
**
2 1
3 4
5 6
8 7
10 IBM ServeRAID-3H, ServeRAID-3HB, and ServeRAID-3L, Controllers