Sun Microsystems Sun Enterprise Server User Guide

Sun Enterprise Server ™ Alternate

Pathing 2.3.1 User Guide

Sun Microsystems, Inc.
901 San Antonio Road
Palo Alto,CA 94303-4900
U.S.A. 650-960-1300

Part No. 806-4150-10
September 2000, Revision A

Send comments about this document to: [e-mail]

Copyright 2000 Sun Microsystems, Inc., 901 San Antonio Road, Palo Alto, California 94303-4900
U.S.A. All rights reserved.

This product ordocument isprotected bycopyright and distributedunder licensesrestricting itsuse, copying,distribution, and decompilation.
No partof thisproduct ordocument maybe reproducedin anyform byany means withoutprior writtenauthorization ofSun and itslicensors,
if any.Third-party software,including fonttechnology,is copyrightedand licensedfrom Sunsuppliers.

Parts ofthe productmay bederived fromBerkeley BSDsystems, licensedfrom theUniversity of California.UNIX isa registeredtrademark in
the U.S.and othercountries, exclusivelylicensed throughX/Open Company, Ltd.For NetscapeCommunicator™, thefollowing notice applies:
(c) Copyright1995 NetscapeCommunications Corporation.All rightsreserved.

Sun, SunMicrosystems, theSun logo,AnswerBook2, docs.sun.com,Sun Enterprise,OpenBoot, and Solarisare trademarks,registered
trademarks, orservice marksof SunMicrosystems, Inc.in theU.S. and othercountries. AllSPARCtrademarks areused underlicense and are
trademarks orregisteredtrademarks of SPARCInternational, Inc.in the U.S.and othercountries. Productsbearing SPARC trademarksare
based uponan architecturedeveloped bySun Microsystems,Inc.

The OPENLOOK andSun™ GraphicalUser Interfacewas developed bySun Microsystems,Inc. forits usersand licensees. Sun acknowledges
the pioneeringefforts ofXerox inresearchingand developing theconcept ofvisual orgraphical user interfaces for thecomputer industry.Sun
holds anon-exclusive licensefrom Xeroxto theXerox GraphicalUser Interface,which licensealso covers Sun’slicensees whoimplement OPEN
LOOK GUIsand otherwisecomply withSun’s writtenlicense agreements.

RESTRICTEDRIGHTS:Use, duplication,or disclosureby theU.S. Governmentis subject torestrictions ofFAR52.227-14(g)(2)(6/87) andFAR

52.227-19(6/87), orDFAR252.227-7015(b)(6/95) andDFAR227.7202-3(a).
DOCUMENTATIONIS PROVIDED “ASIS” ANDALL EXPRESSOR IMPLIEDCONDITIONS, REPRESENTATIONSAND WARRANTIES,

INCLUDING ANYIMPLIED WARRANTYOF MERCHANTABILITY,FITNESS FORA PARTICULARPURPOSE OR NON-INFRINGEMENT,
ARE DISCLAIMED,EXCEPT TOTHE EXTENTTHATSUCH DISCLAIMERSARE HELD TOBE LEGALLYINVALID.

Copyright 2000Sun Microsystems,Inc., 901San AntonioRoad, PaloAlto, Californie 94303Etats-Unis. Tous droits réservés.
Ce produitou documentest protégépar uncopyright etdistribué avecdes licences quien restreignentl’utilisation, lacopie, ladistribution, etla

décompilation. Aucunepartie dece produitou documentne peutêtre reproduitesous aucuneforme, parquelque moyen quece soit,sans
l’autorisation préalableet écritede Sunet deses bailleurs delicence, s’ily ena. Lelogiciel détenu pardes tiers,et quicomprend latechnologie
relativeaux polices decaractères, estprotégé parun copyrightet licenciépar desfournisseurs de Sun.

Des partiesde ceproduit pourrontêtre dérivéesdes systèmesBerkeley BSDlicenciés parl’Université de Californie.UNIX estune marque
déposée auxEtats-Unis etdans d’autrespays etlicenciée exclusivementpar X/Open Company,Ltd. Lanotice suivante est applicable à
Netscape Communicator™:(c) Copyright1995 NetscapeCommunications Corporation.Tousdroits réservés.

Sun, SunMicrosystems, lelogo Sun,AnswerBook2, docs.sun.com,Sun Enterprise,OpenBoot, et Solarissont desmarques defabrique oudes
marquesdéposées, ou marquesde service,de SunMicrosystems, Inc.aux Etats-Uniset dansd’autres pays. Toutes les marques SPARC sont
utilisées souslicence etsont desmarques defabrique oudes marquesdéposées de SPARCInternational, Inc. aux Etats-Unis etdans d’autres
pays. Lesproduits portantles marquesSPARCsont baséssur unearchitecture développéepar SunMicrosystems, Inc.

L’interfaced’utilisation graphiqueOPEN LOOKet Sun™a été développéepar SunMicrosystems, Inc.pour sesutilisateurs et licenciés. Sun
reconnaîtles effortsde pionniers deXerox pourla rechercheet ledéveloppement duconcept desinterfaces d’utilisation visuelle ou graphique
pour l’industriede l’informatique.Sun détientune licencenon exclusive deXerox surl’interface d’utilisationgraphique Xerox,cette licence
couvrant égalementles licenciésde Sunqui mettenten place l’interfaced’utilisation graphiqueOPEN LOOKet qui en outre seconforment aux
licences écritesde Sun.

CETTE PUBLICATIONEST FOURNIE "ENL’ETAT"ET AUCUNEGARANTIE, EXPRESSEOU IMPLICITE,N’EST ACCORDEE, YCOMPRIS
DES GARANTIESCONCERNANT LAVALEURMARCHANDE, L’APTITUDE DELA PUBLICATION AREPONDRE AUNE UTILISATION
PARTICULIERE, OULE FAIT QU’ELLENE SOITPASCONTREFAISANTEDE PRODUITDE TIERS. CEDENI DEGARANTIE NE
S’APPLIQUERAIT PAS,DANS LAMESURE OU ILSERAIT TENUJURIDIQUEMENT NULET NONAVENU.

Sun Enterprise10000 SSPAttributions:
This software iscopyrighted bythe Regents ofthe Universityof California, SunMicrosystems, Inc.,and otherparties. The following terms

apply toall filesassociated withthe softwareunless explicitly disclaimedin individual files.

Please

Recycle

The authorshereby grantpermission touse, copy,modify,distribute, and licensethis softwareand its documentationfor anypurpose,
provided thatexisting copyrightnotices areretained inall copies andthat thisnotice isincluded verbatim inany distributions.No written
agreement, license,or royaltyfee isrequired forany ofthe authorized uses. Modifications tothis softwaremay becopyrighted by theirauthors
and neednot followthe licensingterms describedhere, providedthat the newterms areclearly indicated onthe firstpage ofeach file where
they apply.

Contents

Preface xi

How This Book Is Organized xi
Before You Read This Book xii
Using UNIX Commands xii
Typographic Conventions xiii
Shell Prompts xiii
Ordering Sun Documentation xiv
Related Documentation xiv
Sun Documentation on the Web xiv
Sun Welcomes Your Comments xv

1. Introduction to Alternate Pathing 1

Purpose of Alternate Pathing 1
Basic Alternate Pathing Concepts 4

Physical Path 5
Metadisk 5

Path Optimization on a Sun StorEdge T3 Disk 6

Metanetwork 6
Disk Path Group 7

v

Network Path Group 9

Supported Software Versions 10
AP Configuration Examples 11
AP and Domains 12

2. Alternate Pathing Database 13

Managing Copies of the Database 13
Locating Databases to Maximize RAS 14
Creating and Deleting Databases 15

▼ To Create a Copy of the AP Database 15
▼ To Delete a Copy of the AP Database 16

Viewing Database Information 16

▼ To View Information About Database Copies 17

Viewing Path Group Information 17

▼ To View Uncommitted Disk Entries 18
▼ To View Committed Disk Entries 18
▼ To View Uncommitted Network Entries 19
▼ To View Committed Network Entries 19

3. Using Metadisks and Disk Path Groups 21

Device Nodes for Metadisks 21
Automatic Switching of Metadisks 22
Disk Availability and Performance Trade-Offs 24
Disk Mirroring Considerations 25
Working With Disk Path Groups and Metadisks 29

▼ To Create a Disk Path Group and Metadisk 29
▼ To Switch From the Primary Path to the Alternate Path 32
▼ To Switch Back to the Primary Path 35
▼ To Delete Disk Path Groups and Metadisks 36

vi Sun Enterprise Server Alternate Pathing 2.3.1 User Guide • September 2000

▼ To Deconfigure a Metadisk 38
▼ To Reconfigure a Metadisk 38

4. Using AP Boot Devices 39

Placing the Boot Disk Under AP Control 39

▼ To Place a Boot Disk Under AP Control 39
▼ To Alternately Path a Mirrored Boot Disk 41
▼ To Remove a Mirrored Boot Disk From AP Control 42
▼ To Remove the Boot Disk From AP Control 42

AP Boot Sequence 43
Using Single-User Mode 43

5. Using Metanetworks and
Network Path Groups 45

Metanetwork Interfaces 45
Working With Network Path Groups 46

▼ To Create a Network Path Group and Metanetwork 46
▼ To Switch a Network Path Group 50
▼ To Delete a Network Path Group and Metanetwork 51
▼ To Deconfigure a Metanetwork 51
▼ To Reconfigure a MetaNetwork 52

Alternately Pathing the Primary Network Interface 53
Configuring AP for a Current Network 54

▼ To Create a Network Path Group and Metanetwork for the Primary

Network 54

▼ To Delete the Network Path Group and Metanetwork for the Primary

Network 55

▼ To Deconfigure the Metanetwork for the Primary Network 56
▼ To Reconfigure the Metanetwork for the Primary Network 56

Contents vii

6. Interaction Between AP and DR 59

Using DR and AP Together 59
Maintaining the Correct AP State 61

A. AP Components 63

B. AP man pages 65

C. Driver Layers 67

Glossary 69

viii Sun Enterprise Server Alternate Pathing 2.3.1 User Guide • September 2000

Figures

FIGURE 1-1 Alternately Pathed I/O Device 2
FIGURE 1-2 Switching Paths After an I/O Controller Failure 3
FIGURE 1-3 Switching Paths for a DR Detach Operation 4
FIGURE 1-4 Physical Path 5
FIGURE 1-5 Metadisk Example 6
FIGURE 1-6 Metanetwork 7
FIGURE 1-7 Disk Path Group Switch 8
FIGURE 1-8 Network Path Group 10
FIGURE 1-9 Typical AP Configuration 11
FIGURE 1-10 AP and Disk Mirroring 12
FIGURE 3-1 System Boards and Disk Controllers 25
FIGURE 3-2 System Boards and Controllers 26
FIGURE 3-3 Mirrored Volumes Example 1 26
FIGURE 3-4 Mirrored Volumes Example 2 27
FIGURE 3-5 Mirrored Volumes Example 3 28
FIGURE C-1 AP Disk Driver Layers 67
FIGURE C-2 AP Network Driver Layers 68

ix

x Sun Enterprise Server Alternate Pathing 2.3.1 User Guide • September 2000

Preface

The Sun Enterprise Server Alternate Pathing 2.3.1 User Guide describes the alternate
pathing (AP) component of the Sun Enterprise™ server product line. Some AP
features apply only to the Sun Enterprise 10000 server, and are noted throughout
this guide.

How This Book Is Organized

This guide contains the following chapters:
Chapter 1 introduces AP.
Chapter 2 covers the AP database operations.
Chapter 3 describes metadisks and disk path groups, and explains how to use them.
Chapter 4 covers unattended system boot issues.
Chapter 5 describes metanetworks and network path groups, and explains how to

use them.
Chapter 6 describes how dynamic reconfiguration (DR) and AP work together.
Appendix A provides a list of all AP commands.
Appendix B provides an overview of the underlying AP architecture.
Appendix C provides an overview of the underlying AP drivers.

xi

Before You Read This Book

This manual is intended for the Sun Enterprise system administrator, who has a
working knowledge of UNIX® systems, particularly those based on the Solaris™
operating environment. If you do not have such knowledge, read the Solaris User
and System Administrator AnswerBook™ documentation provided with this
system, and consider UNIX system administration training.

Using UNIX Commands

This document does not contain information on basic UNIX commands and
procedures such as shutting down the system, booting the system, and configuring
devices.

See one or more of the following for this information:

■ AnswerBook online documentation for the Solaris software environment,

particularly those dealing with Solaris system administration

■ Other software documentation that you received with your system

xii Sun Enterprise Server Alternate Pathing 2.3.1 User Guide • September 2000

Typographic Conventions

TABLEP-1 Typographic Conventions

Typeface or
Symbol

AaBbCc123 The names of commands, files,

AaBbCc123 What you type, when

AaBbCc123 Book titles, new words or terms,

Meaning Examples

Edit your .login file.
and directories; on-screen
computer output.

contrasted with on-screen
computer output.

words to be emphasized.
Command-line variable; replace
with a real name or value.

Use ls -a to list all files.

% You have mail.

% su

Password:

Read Chapter 6 in the User Guide.

These are called class options.

You must be root to do this.

To delete a file, type rm filename.

Shell Prompts

TABLEP-2 Shell Prompts

Shell Prompt

C shell machine_name%
C shell superuser machine_name#
Bourne shell and Korn shell $
Bourne shell and Korn shell superuser #

Ordering Sun Documentation

Fatbrain.com, an Internet professional bookstore, stocks select product
documentation from Sun Microsystems, Inc.

Preface xiii

For a list of documents and how to order them, visit the Sun Documentation Center
on Fatbrain.com at:

http://www1.fatbrain.com/documentation/sun

Related Documentation

TABLEP-3 Related Documentation

Application Title

Installation Solaris 8 01/01 Sun Hardware Platform Guide
Reference (man pages) Sun Enterprise Server Alternate Pathing 2.3.1 Reference Manual
Release Notes Release Notes Supplement Solaris 8 01/01
Other Sun Enterprise 10000 Dynamic Reconfiguration User Guide

Sun Enterprise 6x00, 5x00, 4x00, 3x00 Dynamic Reconfiguration
User Guide
Sun Enterprise 10000 Dynamic Reconfiguration Reference Manual

Sun Documentation on the Web

The docs.sun.comSMweb site enables you to access Sun technical documentation
on the Web. You can browse the docs.sun.com archive or search for a specific book
title or subject at:

http://docs.sun.com

Sun Welcomes Your Comments

We are interested in improving our documentation and welcome your comments
and suggestions. You can email your comments to us at:

[e-mail]

xiv Sun Enterprise Server Alternate Pathing 2.3.1 User Guide • September 2000

Please include the part number of your document in the subject line of your email.

Preface xv

xvi Sun Enterprise Server Alternate Pathing 2.3.1 User Guide • September 2000

CHAPTER

1

Introduction to Alternate Pathing

This chapter describes the basic purpose of alternate pathing and provides an
overview of alternate pathing concepts and terminology.

Purpose of Alternate Pathing

Alternate pathing (AP) supports high availability of I/O controllers—the hardware
components that reside on system boards and enable the Sun Enterprise server to
communicate with I/O devices such as disks and networks. With AP, each I/O
device connects to two I/O controllers.

1

Sun Enterprise Ser ver

I/O

I/O controller

Active path
(I/O flows
here)

Passive path

(no I/O)

I/O device

FIGURE 1-1 Alternately Pathed I/O Device

System board

The I/O controllers are part of two separate electrical pathways to the I/O device,
known as alternate paths. AP enables you to set up and use alternate paths on the Sun
Enterprise servers.

For disk controllers, this switch occurs automatically whenever a path failure is
detected during normal operation. For network controllers, you must manually
switch paths (using a single AP command).

There are two purposes for AP. One purpose is to help protect against I/O controller
failures. With AP, if one I/O controller fails, you can switch to the alternate
controller.

For disk metadevices on a Sun StorEdge™ T3 disk; where two viable physical I/O
device paths are present, path optimization is applied to a disk pathgroup. Path
optimization refers to the efficient distribution of I/O traffic for a particular device.
If one of the physical I/O device paths becomes unavailable, whether due to device
failure or user action, path optimization is disabled.

2 Sun Enterprise Server Alternate Pathing 2.3.1 User Guide • September 2000

I/O controller

problem

Active path

(unavailable)

Sun Enterprise Ser ver

I/O

FIGURE 1-2 Switching Paths After an I/O Controller Failure

Sun Enterprise Server

I/O

New active
path

Note – Automatic switching, on a T3, disables the path optimization algorithm,

since only one path is available.

The second purpose of AP is to support dynamic reconfiguration (DR). DR is used to
logically attach and detach system boards from the operating system without having
to halt and reboot.

For example, with DR you can detach a board from the operating system, physically
remove and service the board, and then re-insert the board and attach it to the
operating system again. You can do all of this without halting the operating system
or terminating any user applications.

If you want to detach a board that is connected to an I/O device, and if that I/O
device is alternately pathed, you must first use AP to redirect the I/O flow to a
controller on a different board.

For T3 disk path groups this action disables path optimization, allowing the DR
detach of the inactive path. You can then use DR to detach the system board without
interrupting the I/O flow.

Chapter 1 Introduction to Alternate Pathing 3

On the Sun Enterprise 10000, the switch can occur automatically during the DR
operation (for both disk and network devices), assuming a viable alternate controller
exists on another board. However, a manual switch is preferred to disable path
optimization prior to issuing a DR detach.

On all other servers, the switch must be performed manually.
The following figure shows the relationship between AP and DR.

Active path
(unavailable)

Sun Enterprise Server

I/O

FIGURE 1-3 Switching Paths for a DR Detach Operation

Sun Enterprise Ser ver

DR Detach,
and hot-swap

I/O

Active path

(new)

Basic Alternate Pathing Concepts

This section discusses basic AP concepts and introduces the terminology that is used
throughout this chapter.

4 Sun Enterprise Server Alternate Pathing 2.3.1 User Guide • September 2000

Physical Path

For the purposes of AP, an I/O device is either a disk or network. An I/O controller is
the controller card for an I/O device. An I/O port is a connector on a controller card.
Often there are two or more ports per controller card. A device node is a path in the

/devices or /dev directories that is used to specify a physical device, for example,
/dev/dsk/c0t0d1s0. The term physical path refers to the electrical path from the

host to a disk or network.

Sun Enterprise Ser ver

I/O

System board

and I/O controllers

I/O device

Physical path

FIGURE 1-4 Physical Path

You reference a physical device by means of a device node, for example, /dev/dsk/
c0t1d1s0.

Metadisk

A metadisk , as illustrated in FIGURE 1-5, is a construct that enables you to access a disk
by using either of two physical paths without having to reference either path
explicitly within your scripts and programs.

You reference a metadisk, in your scripts and programs, using an AP-specific device
node such as /dev/ap/dsk/mc0t1d1s0. See “Device Nodes for Metadisks” on
page 21 for more information.

Chapter 1 Introduction to Alternate Pathing 5

In the following figure, an AP-specific device node is used to perform disk I/O,
regardless of which pln port (pln:2 or pln:9) is currently handling I/O.

Sun Enterprise Server

/dev/ap/dsk/mc0t1d1s0

System boards

pln:2

I/O

FIGURE 1-5 Metadisk Example

SSA

pln:9

SPARCstorage
Array (SSA) controllers
with one or two PLN
ports. (Black PLN ports
are connected to the SSA.)

SSA port

Path Optimization on a Sun StorEdge T3 Disk

At system startup for a T3, a path optimization algorithm is executed for disk path
groups, whenever two functioning physical paths to the device are available.
Disabling one of the physical paths through device failure or user action turns off
path optimization for the affected disk path group. Users restart the path
optimization algorithm using the apconfig(1M) command, or by performing a
system reboot. Path optimization cannot be re-enabled until both physical I/O paths
are available. For more information see “Working With Disk Path Groups and
Metadisks” on page 29.

Metanetwork

A metanetwork, as illustrated in FIGURE 1-6, is a construct that enables you to access a
network by using either of two physical paths without having to reference either
path explicitly within your scripts and programs. You reference a metanetwork, in
your scripts and programs, using a metanetwork interface name such as mether1. See
“Metanetwork Interfaces” on page 45 for more information.

6 Sun Enterprise Server Alternate Pathing 2.3.1 User Guide • September 2000

In the following figure, mether1 is used to access a metanetwork, regardless of
which controller (hme1 or qfe3) is currently processing I/O for the metanetwork.

Sun Enterprise Ser ver

mether1

System boards
and controllers

hme0

hme1

hme2

hme3

qfe0

qfe1

qfe2

qfe3

I/O

Network

FIGURE 1-6 Metanetwork

Disk Path Group

A disk path group, as illustrated in FIGURE 1-7, consists of two physical paths leading
to the same disk array. When a physical path is part of a path group, it is called an
alternate path. An alternate path to a disk can be uniquely identified by the pln port
or sf port that the alternate path uses. The alternate path that is currently handling
I/O is called the active alternate.

Note – When a T3 disk path group is actively executing the path optimization

algorithm, both physical paths are marked as active alternate s. The loss of a physical
path, for whatever reason, disables path optimization. In that situation, only one
path will be marked as an active alternate.

Note that whereas a metadisk (for example, /dev/ap/[r]dsk/mc?t?d?s?) provides a
means for you to access an individual disk, in your scripts and programs, a disk path
group provides a means for you to manipulate the path to that disk when you run
AP commands. For example, to perform a switch operation, that is, change the active
alternate from one alternate path to another, you reference a disk path group with an
apconfig(1M) command.

Chapter 1 Introduction to Alternate Pathing 7

Note – Initiating a switch operation automatically disables path optimization on the

T3.

One of the alternate paths is designated as the primary path. Although the active
alternate changes when you perform a switch operation, the primary path remains
constant. You reference a disk path group by specifying the pln port (for example,
pln:2)orsf port (for example, sf:2) that corresponds to the primary path. For
information about determining the pln or sf port name, see “Device Nodes for
Metadisks” on page 21.

To switch the active alternate of a disk path group, use:

# apconfig -P sf:2 -a sf:9

The following figure is an example of the results of using the apconfig(1M)
command to switch the active alternate of a disk path group.

Sun Enterprise Ser ver

sf:2

I/O

System boards

sf:2 sf:9

and controllers

Switch

Alternate path
(primary path)

Disk array

FIGURE 1-7 Disk Path Group Switch

8 Sun Enterprise Server Alternate Pathing 2.3.1 User Guide • September 2000

Alternate path

(active alternate)

Note – This action disables path optimization on the T3. To re-enable path

optimization use:

# apconfig -P sf:2 -a sf:2 -a sf:9

Network Path Group

A network path group, as illustrated in FIGURE 1-8 consists of two network controllers
connected to the same physical network. The terms alternate path, active alternate, and
switch have basically the same meaning as they do for disk path groups. However,
there is no primary path in a network path group.

To specify a network path group, reference the corresponding metanetwork interface
name, for example, mether1. Metanetwork interface names are described in
“Metanetwork Interfaces” on page 45. To switch the active alternate of a network
pathgroup, use:

#apconfig -a mether1 -a hme1

For example,
switch the active alternate of a network path group.

FIGURE 1-8 shows the results of using the apconfig(1M) command to

Chapter 1 Introduction to Alternate Pathing 9

Sun Enterprise Ser ver

mether1

System boards

and controllers

I/O

hme0

Alternate Path

hme1

hme2

hme3

Switch

qfe0

qfe1

qfe2

qfe3

Alternate Path
(active alternate)

Network

FIGURE 1-8 Network Path Group

Supported Software Versions

AP 2.3.1 supports the Solaris 2.6, Solaris 7, and Solaris 8 operating environments.
The disks, network devices and third party software products supported by AP are

listed in the
If you have created alternate paths to your disks, and you also use a volume

manager with those disks, the disks must be known to the volume manager,
exclusively, by their AP metadisk names. This requirement enables AP to switch the
active path without interfering with the volume manager.

You can place the boot disk and the primary network interface under AP control. AP
makes it possible for the system to boot unattended even if the primary network or
boot disk controller is not accessible, as long as viable alternate paths for these
devices are defined.

Release Notes Supplement Solar is 8 01/01.

10 Sun Enterprise Server Alternate Pathing 2.3.1 User Guide • September 2000

AP Configuration Examples

FIGURE 1-9 shows how you can use AP to support an Ethernet network and a disk

array.

Backplane

Board 1

SBus
I/F

FIGURE 1-9 Typical AP Configuration

SBus

Ethernet

Board 2

SBus
I/F

SBus

SBus controllers

Fibre channel

In this example, two network controllers—one each on Board 1 and Board 2—are
connected to the same network. Similarly, two SSA controllers on the two boards are
connected to the same SSA. In this situation, if Board 1 is detached with a DR Detach
operation, AP can switch usage to Board 2 without interfering with any I/O
operations that may be in progress.

AP is not equivalent to disk mirroring. Disk mirroring primarily achieves data
redundancy although two paths are available, one for each side of the mirror.

AP achieves true pathing redundancy, by making two paths available for each side of
the mirror. To use AP and disk mirroring together, you must configure your volume
manager software (such as Sun Enterprise Volume Manager™ (SEVM)) so that it
uses the AP metadisk paths.

The following figure shows an example of how AP can be used in conjunction with
disk mirroring.

Chapter 1 Introduction to Alternate Pathing 11

Backplane

Board 1

SBus
I/F

SSA

FIGURE 1-10 AP and Disk Mirroring

SBus

Mirrored

Board 2

SBus
I/F

Fibre
channels

SBus

SBus

controllers

SSA

This type of configuration enables you to switch the paths used to implement the
mirror from one board to another board, without disrupting the disk mirroring or
any active I/O.

AP and Domains

All Sun Enterprise servers support domains. The Sun Enterprise 10000 server
supports dynamic system domains. However, AP cannot be used across two
domains.

For example, suppose a board contains a controller that is part of a path group, and
you move that board into a different domain using DR. You can do this only if the
alternate path on that board is not currently active. In this case, you can no longer
switch to the alternate path on that board.

12 Sun Enterprise Server Alternate Pathing 2.3.1 User Guide • September 2000