Red Hat DEVICE-MAPPER MULTIPATH 4.6 Instruction Manual

Using Device-Mapper Multipath
Configuration and
Administration
4.6
DM_Multipath
ISBN: N/A
Publication date: July 2008

This book provides information on using the Device-Mapper Multipath feature of Red Hat
Enterprise Linux 4.6
Using Device-Mapper Multipath

Using Device-Mapper Multipath: Configuration and
Administration
Copyright ©2008 Red Hat, Inc.
Copyright ©2008 Red Hat, Inc. This material may only be distributed subject to the terms and conditions set forth in the
Open Publication License, V1.0 or later with the restrictions noted below (the latest version of the OPL is presently
available at http://www.opencontent.org/openpub/).
Distribution of substantively modified versions of this document is prohibited without the explicit permission of the
copyright holder.
Distribution of the work or derivative of the work in any standard (paper) book form for commercial purposes is
prohibited unless prior permission is obtained from the copyright holder.
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.
The GPG fingerprint of the [email protected] key is:
CA 20 86 86 2B D6 9D FC 65 F6 EC C4 21 91 80 CD DB 42 A6 0E
1801 Varsity Drive
Raleigh, NC 27606-2072
USA
Phone: [phone]
Phone: [phone]
Fax: [phone]
PO Box 13588
Research Triangle Park, NC 27709
USA

Using Device-Mapper Multipath

Preface ....................................................................................................................vii
1. Audience ...................................................................................................... vii
2. Related Documentation ................................................................................. vii
3. Feedback .................................................................................................... viii
4. Document Conventions ................................................................................ viii
1. Device Mapper Multipathing .................................................................................... 1
1. Overview of DM-Multipath ............................................................................... 1
2. Storage Array Support .................................................................................... 4
3. DM-Multipath Components ............................................................................. 4
4. DM-Multipath Setup Overview ......................................................................... 5
2. Multipath Devices ................................................................................................... 7
1. Multipath Device Identifiers ............................................................................. 7
2. Consistent Multipath Device Names in a Cluster .............................................. 7
3. Multipath Device Attributes ............................................................................. 8
4. Multipath Devices in Logical Volumes .............................................................. 8
3. Setting Up DM-Multipath ........................................................................................11
1. Setting Up DM-Multipath ................................................................................11
2. Ignoring Local Disks when Generating Multipath Devices ................................12
3. Adding Devices to the Multipathing Database .................................................14
4. The DM-Multipath Configuration File ......................................................................15
1. Configuration File Overview ...........................................................................15
2. Configuration File Blacklist .............................................................................16
2.1. Blacklisting by WWID .........................................................................16
2.2. Blacklisting By Device Name ...............................................................17
3. Configuration File Defaults .............................................................................17
4. Multipaths Device Configuration Attributes ......................................................20
5. Configuration File Devices .............................................................................22
5. DM-Multipath Administration and Troubleshooting ...................................................27
1. Multipath Command Output ...........................................................................27
2. Multipath Queries with multipath Command ....................................................28
3. Multipath Command Options ..........................................................................28
4. Determining Device Mapper Entries with the dmsetup Command .....................29
5. Troubleshooting with the multipathd Interactive Console ..................................29
Index .......................................................................................................................31
v

vi

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.
vii

•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
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)-4.6 (2008-07-31T15:20)
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
Certain words in this manual are represented in different fonts, styles, and weights. This
highlighting indicates that the word is part of a specific category. The categories include the
following:
Courier font
Courier font represents commands,file names and paths, and prompts .
When shown as below, it indicates computer output:
Desktop about.html logs paulwesterberg.png
Mail backupfiles mail reports
bold Courier font
Bold Courier font represents text that you are to type, such as: service jonas start
Preface
viii

If you have to run a command as root, the root prompt (#) precedes the command:
#gconftool-2
italic Courier font
Italic Courier font represents a variable, such as an installation directory:
install_dir/bin/
bold font
Bold font represents application programs and text found on a graphical interface.
When shown like this: OK , it indicates a button on a graphical application interface.
Additionally, the manual uses different strategies to draw your attention to pieces of information.
In order of how critical the information is to you, these items are marked as follows:
Note
A note is typically information that you need to understand the behavior of the
system.
Tip
A tip is typically an alternative way of performing a task.
Important
Important information is necessary, but possibly unexpected, such as a
configuration change that will not persist after a reboot.
Caution
A caution indicates an act that would violate your support agreement, such as
recompiling the kernel.
Document Conventions
ix

Warning
A warning indicates potential data loss, as may happen when tuning hardware
for maximum performance.
Preface
x