Red Hat ENTERPRISE LINUX 4 - DM MULTIPATH Manuale utente

Red Hat Enterprise Linux 4

DM Multipath

DM Multipath Configuration and Administration

DM Multipath

Red Hat Enterprise Linux 4 DM Multipath

DM Multipath Configuration and Administration

Edition 1.0

conditions set forth in the Open Publication License, V1.0 or later (the latest version of the OPL is

presently available at http://www.opencontent.org/openpub/).

Red Hat and the Red Hat "Shadow Man" logo are registered trademarks of Red Hat, Inc. in the United

States and other countries.

All other trademarks referenced herein are the property of their respective owners.

1801 Varsity Drive

Raleigh, NC 27606-2072 USA

Phone: +1 919 754 3700

Phone: 888 733 4281

Fax: +1 919 754 3701

PO Box 13588 Research Triangle Park, NC 27709 USA

This book provides information on using the Device-Mapper Multipath feature of Red Hat Enterprise

Linux 4.

iii

Preface v

1. Audience ........................................................................................................................ v

2. Related Documentation ................................................................................................... v

3. Feedback ....................................................................................................................... vi

4. Document Conventions ................................................................................................... vi

4.1. Typographic Conventions ..................................................................................... vi

4.2. Pull-quote Conventions ....................................................................................... viii

4.3. Notes and Warnings ........................................................................................... viii

1. Device Mapper Multipathing 1

1.1. Overview of DM-Multipath ............................................................................................. 1

1.2. Storage Array Support .................................................................................................. 3

1.3. DM-Multipath Components ............................................................................................ 3

1.4. DM-Multipath Setup Overview ....................................................................................... 4

2. Multipath Devices 5

2.1. Multipath Device Identifiers ........................................................................................... 5

2.2. Consistent Multipath Device Names in a Cluster ............................................................ 5

2.3. Multipath Device Attributes ........................................................................................... 6

2.4. Multipath Devices in Logical Volumes ............................................................................ 6

3. Setting Up DM-Multipath 7

3.1. Setting Up DM-Multipath ............................................................................................... 7

3.2. Ignoring Local Disks when Generating Multipath Devices ................................................ 8

3.3. Adding Devices to the Multipathing Database ............................................................. 10

4. The DM-Multipath Configuration File 11

4.1. Configuration File Overview ........................................................................................ 11

4.2. Configuration File Blacklist .......................................................................................... 12

4.2.1. Blacklisting by WWID ....................................................................................... 12

4.2.2. Blacklisting By Device Name ............................................................................ 12

4.3. Configuration File Defaults .......................................................................................... 13

4.4. Multipaths Device Configuration Attributes ................................................................... 16

4.5. Configuration File Devices .......................................................................................... 18

5. DM-Multipath Administration and Troubleshooting 21

5.1. Multipath Command Output ........................................................................................ 21

5.2. Multipath Queries with multipath Command ................................................................. 22

5.3. Multipath Command Options ....................................................................................... 22

5.4. Determining Device Mapper Entries with the dmsetup Command ................................... 23

5.5. Troubleshooting with the multipathd Interactive Console ............................................... 23

5.6. Resizing an Online Multipathed Device (RHEL 4.8 and later) ......................................... 24

A. Revision History 27

Index 29

Preface

This book describes the Device Mapper Multipath (DM-Multipath) feature of Red Hat Enterprise Linux.

1. Audience

This book is intended to be used by system administrators managing systems running the Linux

operating system. It requires familiarity with Red Hat Enterprise Linux.

2. Related Documentation

For more information about using Red Hat Enterprise Linux, refer to the following resources:

•Red Hat Enterprise Linux Installation Guide — Provides information regarding installation of Red

Hat Enterprise Linux.

•Red Hat Enterprise Linux Introduction to System Administration — Provides introductory information

for new Red Hat Enterprise Linux system administrators.

•Red Hat Enterprise Linux System Administration Guide — Provides more detailed information about

configuring Red Hat Enterprise Linux to suit your particular needs as a user.

•Red Hat Enterprise Linux Reference Guide — Provides detailed information suited for more

experienced users to reference when needed, as opposed to step-by-step instructions.

•Red Hat Enterprise Linux Security Guide — Details the planning and the tools involved in creating a

secured computing environment for the data center, workplace, and home.

For more information about Red Hat Cluster Suite for Red Hat Enterprise Linux, refer to the following

resources:

•Red Hat Cluster Suite Overview — Provides a high level overview of the Red Hat Cluster Suite.

•Configuring and Managing a Red Hat Cluster — Provides information about installing, configuring

and managing Red Hat Cluster components.

•Global File System: Configuration and Administration — Provides information about installing,

configuring, and maintaining Red Hat GFS (Red Hat Global File System).

•LVM Administrator's Guide: Configuration and Administration — Provides a description of the

Logical Volume Manager (LVM), including information on running LVM in a clustered environment.

•Using GNBD with Global File System — Provides an overview on using Global Network Block

Device (GNBD) with Red Hat GFS.

•Linux Virtual Server Administration — Provides information on configuring high-performance

systems and services with the Linux Virtual Server (LVS).

•Red Hat Cluster Suite Release Notes — Provides information about the current release of Red Hat

Cluster Suite.

Red Hat Cluster Suite documentation and other Red Hat documents are available in HTML and PDF

versions online at the following location:

http://www.redhat.com/docs

Preface

3. Feedback

If you spot a typo, or if you have thought of a way to make this manual better, we would love to

hear from you. Please submit a report in Bugzilla (http://bugzilla.redhat.com/bugzilla/) against the

component rh-cs.

Be sure to mention the manual's identifier:

rh-MPIO(EN)-4.8 (2009-05-13T12:48)

By mentioning this manual's identifier, we know exactly which version of the guide you have.

If you have a suggestion for improving the documentation, try to be as specific as possible. If you have

found an error, please include the section number and some of the surrounding text so we can find it

easily.

4. Document Conventions

This manual uses several conventions to highlight certain words and phrases and draw attention to

specific pieces of information.

In PDF and paper editions, this manual uses typefaces drawn from the Liberation Fonts1 set. The

Liberation Fonts set is also used in HTML editions if the set is installed on your system. If not,

alternative but equivalent typefaces are displayed. Note: Red Hat Enterprise Linux 5 and later includes

the Liberation Fonts set by default.

4.1. Typographic Conventions

Four typographic conventions are used to call attention to specific words and phrases. These

conventions, and the circumstances they apply to, are as follows.

Mono-spaced Bold

Used to highlight system input, including shell commands, file names and paths. Also used to highlight

key caps and key-combinations. For example:

To see the contents of the file my_next_bestselling_novel in your current

working directory, enter the cat my_next_bestselling_novel command at the

shell prompt and press Enter to execute the command.

The above includes a file name, a shell command and a key cap, all presented in Mono-spaced Bold

and all distinguishable thanks to context.

Key-combinations can be distinguished from key caps by the hyphen connecting each part of a key-

combination. For example:

Press Enter to execute the command.

Press Ctrl+Alt+F1 to switch to the first virtual terminal. Press Ctrl+Alt+F7 to

return to your X-Windows session.

1 https://fedorahosted.org/liberation-fonts/

Typographic Conventions

vii

The first sentence highlights the particular key cap to press. The second highlights two sets of three

key caps, each set pressed simultaneously.

If source code is discussed, class names, methods, functions, variable names and returned values

mentioned within a paragraph will be presented as above, in Mono-spaced Bold. For example:

File-related classes include filesystem for file systems, file for files, and dir for

directories. Each class has its own associated set of permissions.

Proportional Bold

This denotes words or phrases encountered on a system, including application names; dialogue

box text; labelled buttons; check-box and radio button labels; menu titles and sub-menu titles. For

example:

Choose System > Preferences > Mouse from the main menu bar to launch Mouse

Preferences. In the Buttons tab, click the Left-handed mouse check box and click

Close to switch the primary mouse button from the left to the right (making the mouse

suitable for use in the left hand).

To insert a special character into a gedit file, choose Applications > Accessories

> Character Map from the main menu bar. Next, choose Search > Find… from the

Character Map menu bar, type the name of the character in the Search field and

click Next. The character you sought will be highlighted in the Character Table.

Double-click this highlighted character to place it in the Text to copy field and then

click the Copy button. Now switch back to your document and choose Edit > Paste

from the gedit menu bar.

The above text includes application names; system-wide menu names and items; application-specific

menu names; and buttons and text found within a GUI interface, all presented in Proportional Bold and

all distinguishable by context.

Note the > shorthand used to indicate traversal through a menu and its sub-menus. This is to avoid

the difficult-to-follow 'Select Mouse from the Preferences sub-menu in the System menu of the main

menu bar' approach.

Mono-spaced Bold Italic or Proportional Bold Italic

Whether Mono-spaced Bold or Proportional Bold, the addition of Italics indicates replaceable or

variable text. Italics denotes text you do not input literally or displayed text that changes depending on

circumstance. For example:

To connect to a remote machine using ssh, type ssh username@domain.name at

a shell prompt. If the remote machine is example.com and your username on that

machine is john, type ssh [email protected].

The mount -o remount file-system command remounts the named file

system. For example, to remount the /home file system, the command is mount -o

remount /home.

To see the version of a currently installed package, use the rpm -q package

command. It will return a result as follows: package-version-release.

Note the words in bold italics above — username, domain.name, file-system, package, version and

release. Each word is a placeholder, either for text you enter when issuing a command or for text

displayed by the system.

Preface

viii

Aside from standard usage for presenting the title of a work, italics denotes the first use of a new and

important term. For example:

When the Apache HTTP Server accepts requests, it dispatches child processes

or threads to handle them. This group of child processes or threads is known as

a server-pool. Under Apache HTTP Server 2.0, the responsibility for creating and

maintaining these server-pools has been abstracted to a group of modules called

Multi-Processing Modules (MPMs). Unlike other modules, only one module from the

MPM group can be loaded by the Apache HTTP Server.

4.2. Pull-quote Conventions

Two, commonly multi-line, data types are set off visually from the surrounding text.

Output sent to a terminal is set in Mono-spaced Roman and presented thus:

books Desktop documentation drafts mss photos stuff svn

books_tests Desktop1 downloads images notes scripts svgs

Source-code listings are also set in Mono-spaced Roman but are presented and highlighted as

follows:

package org.jboss.book.jca.ex1;

import javax.naming.InitialContext;

public class ExClient

{

public static void main(String args[])

throws Exception

{

InitialContext iniCtx = new InitialContext();

Object ref = iniCtx.lookup("EchoBean");

EchoHome home = (EchoHome) ref;

Echo echo = home.create();

System.out.println("Created Echo");

System.out.println("Echo.echo('Hello') = " + echo.echo("Hello"));

}

4.3. Notes and Warnings

Finally, we use three visual styles to draw attention to information that might otherwise be overlooked.

Notes and Warnings

Note

A note is a tip or shortcut or alternative approach to the task at hand. Ignoring a note

should have no negative consequences, but you might miss out on a trick that makes your

life easier.

Important

Important boxes detail things that are easily missed: configuration changes that only

apply to the current session, or services that need restarting before an update will apply.

Ignoring Important boxes won't cause data loss but may cause irritation and frustration.

Warning

A Warning should not be ignored. Ignoring warnings will most likely cause data loss.

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