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1、Red Hat Enterprise Linux 5 DM MultipathDM Multipath Configuration and AdministrationEdition 3Red Hat Enterprise Linux 5 DM MultipathDM Multipath Configuration and Administration Edition 3Legal NoticeCopyright © 2013 Red Hat, Inc.This document is licensed by Red Hat under the Creative Commons At

2、tribution-ShareAlike 3.0 Unported License. If you distribute this document, or a modified version of it, you must provide attribution to Red Hat, Inc. and provide a link to the original. If the document is modified, all Red Hat trademarks must be removed.Red Hat, as the licensor of this document, wa

3、ives the right to enforce, and agrees not to assert, Section 4d of CC-BY-SA to the fullest extent permitted by applicable law.Red Hat, Red Hat Enterprise Linux, the Shadowman logo, JBoss, MetaMatrix, Fedora, the Infinity Logo, and RHCE are trademarks of Red Hat, Inc., registered in the United States

4、 and other countries.Linux ® is the registered trademark of Linus Torvalds in the United States and other countries.Java ® is a registered trademark of Oracle and/or its affiliates.XFS ® is a trademark of Silicon Graphics International Corp. or its subsidiaries in the United Statesand

5、/or other countries.MySQL ® is a registered trademark of MySQL AB in the United States, the European Union and other countries.Node.js ® is an official trademark of Joyent. Red Hat Software Collections is not formally related to or endorsed by the official Joyent Node.js open source or com

6、mercial project.The OpenStack ® Word Mark and OpenStack Logo are either registered trademarks/service marks or trademarks/service marks of the OpenStack Foundation, in the United States and other countries and are used with the OpenStack Foundation's permission. We are not affiliated with,

7、endorsed or sponsored by the OpenStack Foundation, or the OpenStack community.All other trademarks are the property of their respective owners.AbstractThis book provides information on using the Device-Mapper Multipath feature of Red Hat Enterprise Linux 5. . . . . . . . . . . . . . . . . . . . . .

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11、. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

12、. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Table of Contents444556788888111112131313141516161718202021212122222327293434343435353636373739Table of Contents12Ta

13、ble of ContentsRed Hat Enterprise Linux 5 DM MultipathPrefaceThis book describes the Device Mapper Multipath (DM-Multipath feature of Red Hat Enterprise Linux for the Red Hat Enterprise Linux 5 release.1. AudienceThis book is intended to be used by system administrators managing systems running the

14、Linux operating system. It requires familiarity with Red Hat Enterprise Linux.2. Related DocumentationFor 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 Enterp

15、rise Linux 5.Red Hat Enterprise Linux Deployment Guide Provides information regarding the deployment, configuration and administration of Red Hat Enterprise Linux 5.For more information about Red Hat Cluster Suite for Red Hat Enterprise Linux 5, refer to the following resources:Red Hat Cluster Suite

16、 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.Logical Volume Manager Administration Provides a description of the Logical Volume Manager (LVM,

17、 including information on running LVM in a clustered environment.Global File System: Configuration and Administration Provides information about installing,configuring, and maintaining Red Hat GFS (Red Hat Global File System.Global File System 2: Configuration and Administration Provides information

18、 about installing, configuring, and maintaining Red Hat GFS2 (Red Hat Global File System 2.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 syst

19、ems 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, PDF, and RPM versions on the Red Hat Enterprise Linux

20、 Documentation CD and online at3. FeedbackBe sure to mention the manual's identifier:Preface 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 fo

21、und an error, please include the section number and some of the surrounding text so we can find it easily.4. Document ConventionsThis 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 use

22、s typefaces drawn from the Liberation Fonts 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 include the Liberation Fonts set by default.4.1. Typo

23、graphic ConventionsFour 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 BoldUsed to highlight system input, including shell commands, file names and paths. Also used to highlight keys

24、 and key combinations. For example:To see the contents of the file my_next_bestselling_novel in your current workingdirectory, enter the cat my_next_bestselling_novel command at the shell promptand press Enter to execute the command.The above includes a file name, a shell command and a key, all pres

25、ented in mono-spaced bold and all distinguishable thanks to context.Key combinations can be distinguished from an individual key by the plus sign that connects each part of a key combination. For example:Press Enter to execute the command.Press Ctrl+Alt+F2 to switch to a virtual terminal.The first e

26、xample highlights a particular key to press. The second example highlights a key combination:a set of three keys 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-sp

27、aced bold. For example: File-related classes include filesystem for file systems, file for files, and dir fordirectories. Each class has its own associated set of permissions.Proportional BoldThis denotes words or phrases encountered on a system, including application names; dialog box text; labeled

28、 buttons; check-box and radio button labels; menu titles and sub-menu titles. For example:Red Hat Enterprise Linux 5 DM MultipathChoose System Preferences Mouse from the main menu bar to launch MousePreferences. In the Buttons tab, select the Left-handed mouse check box and clickClose to switch the

29、primary mouse button from the left to the right (making the mousesuitable 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 theCharacter Map menu bar, type the name of the char

30、acter in the Search field and clickNext. The character you sought will be highlighted in the Character Table. Double-clickthis highlighted character to place it in the Text to copy field and then click the Copybutton. Now switch back to your document and choose Edit Paste from the gedit menubar.The

31、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.Mono-spaced Bold Italic or Proportional Bold ItalicWhether mono-spaced bo

32、ld 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 at a shellprompt. If t

33、he remote machine is and your username on that machine isjohn, type ssh john.The mount -o remount file-system command remounts the named file system. Forexample, 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 -

34、q package command. Itwill return a result as follows: package-version-release.Note the words in bold italics above username, , 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.Aside

35、from standard usage for presenting the title of a work, italics denotes the first use of a new and important term. For example:Publican is a DocBook publishing system.4.2. Pull-quote ConventionsTerminal output and source code listings are set off visually from the surrounding text.Output sent to a t

36、erminal is set in mono-spaced roman and presented thus: Source-code listings are also set in mono-spaced roman but add syntax highlighting as follows:Preface 4.3. Notes and WarningsFinally, we use three visual styles to draw attention to information that might otherwise be overlooked. Chapter 1. Dev

37、ice Mapper MultipathingDevice Mapper Multipathing (DM-Multipath allows you to configure multiple I/O paths between server nodes and storage arrays into a single device. These I/O paths are physical SAN connections that can include separate cables, switches, and controllers. Multipathing aggregates t

38、he I/O paths, creating a new device that consists of the aggregated paths.1.1. New and Changed Features for Red Hat Enterprise Linux 5.7 Red Hat Enterprise Linux 5.7 includes the following documentation and feature updates and changes.The new configuration file parameters fast_io_fail_tmo, dev_loss_

39、tmo, and file_timeout are documented in Chapter 4, The DM-Multipath Configuration File.The procedure for ensuring that multipath devices names are consistent across the nodes in a cluster has been expanded in Section 2.2, “Consistent Multipath Device Names in a Cluster”.1.2. New and Changed Features

40、 for Red Hat Enterprise Linux 5.8 Red Hat Enterprise Linux 5.8 includes the following documentation and feature updates and changes.The getuid_callout and prio_callout configuration file parameters now accept the %cwildcard. For information on the configuration file parameters, see Chapter 4, The DM

41、-Multipath Configuration File.You can now define either the selector or path_selector parameter in the defaults section of the multipath.conf configuration file. Both parameters have the same meaning. For information on the multipath configuration defaults, see Table 4.1, “Multipath Configuration De

42、faults”.1.3. New and Changed Features for Red Hat Enterprise Linux 5.9 Red Hat Enterprise Linux 5.9 includes the following documentation and feature updates and changes.The user_friendly_names and flush_on_last_del multipath configuration parameters can now be defined in the multipaths and devices s

43、ections of the multipath.conf configuration file, as documented in Chapter 4, The DM-Multipath Configuration File.1.4. Overview of DM-MultipathDM-Multipath can be used to provide:RedundancyDM-Multipath can provide failover in an active/passive configuration. In an active/passiveconfiguration, only h

44、alf the paths are used at any time for I/O. If any element of an I/O path (the cable, switch, or controller fails, DM-Multipath switches to an alternate path.Improved PerformanceDM-Multipath can be configured in active/active mode, where I/O is spread over the paths in a round-robin fashion. In some

45、 configurations, DM-Multipath can detect loading on the I/O paths anddynamically re-balance the load.Figure 1.1, “Active/Passive Multipath Configuration with One RAID Device” shows an active/passive configuration with two I/O paths from the server to a RAID device. There are 2 HBAs on the server, 2

46、SAN switches, and 2 RAID controllers. Figure 1.1. Active/Passive Multipath Configuration with One RAID DeviceIn this configuration, there is one I/O path that goes through hba1, SAN1, and controller 1 and a second I/O path that goes through hba2, SAN2, and controller2. There are many points of possi

47、ble failure in this configuration:HBA failureFC cable failureSAN switch failureArray controller port failureWith DM-Multipath configured, a failure at any of these points will cause DM-Multipath to switch to the alternate I/O path.Figure 1.2, “Active/Passive Multipath Configuration with Two RAID Dev

48、ices” shows a more complex active/passive configuration with 2 HBAs on the server, 2 SAN switches, and 2 RAID devices with 2 RAID controllers each. Figure 1.2. Active/Passive Multipath Configuration with Two RAID DevicesIn the example shown in Figure 1.2, “Active/Passive Multipath Configuration with

49、 Two RAID Devices”, there are two I/O paths to each RAID device (just as there are in the example shown in Figure 1.1,“Active/Passive Multipath Configuration with One RAID Device”. With DM-Multipath configured, a failure at any of the points of the I/O path to either of the RAID devices will cause D

50、M-Multipath to switch to the alternate I/O path for that device.Figure 1.3, “Active/Active Multipath Configuration with One RAID Device” shows an active/active configuration with 2 HBAs on the server, 1 SAN switch, and 2 RAID controllers. There are four I/O paths from the server to a storage device:

51、hba1 to controller1hba1 to controller2hba2 to controller1hba2 to controller2In this configuration, I/O can be spread among those four paths. Figure 1.3. Active/Active Multipath Configuration with One RAID Device1.5. Storage Array SupportSome storage arrays require special handling of I/O errors and

52、path switching. These require separate hardware handler kernel modules.1.6. DM-Multipath ComponentsTable 1.1, “DM-Multipath Components”. describes the components of DM-Multipath.Table 1.1. DM-Multipath ComponentsComponent Descriptiondm-multipath kernel module Reroutes I/O and supports failover for p

53、aths and path groups. multipath command Lists and configures multipath devices. Normally started up with/etc/rc.sysinit, it can also be started up by a udev programwhenever a block device is added or it can be run by theinitramfs file system.multipathd daemon Monitors paths; as paths fail and come b

54、ack, it may initiate pathgroup switches. Provides for interactive changes to multipathdevices. This must be restarted for any changes to the/etc/multipath.conf file.kpartx command Creates device mapper devices for the partitions on a device It isnecessary to use this command for DOS-based partitions

55、 with DM-MP. The kpartx is provided in its own package, but the device-mapper-multipath package depends on it.1.7. DM-Multipath Setup OverviewDM-Multipath includes compiled-in default settings that are suitable for common multipath configurations. Setting up DM-multipath is often a simple procedure.

56、The basic procedure for configuring your system with DM-Multipath is as follows:1. Install device-mapper-multipath rpm.2. Edit the multipath.conf configuration file:comment out the default blacklistchange any of the existing defaults as neededsave the configuration file3. Start the multipath daemons

57、.4. Create the multipath device with the multipath command.Detailed setup instructions for several example multipath configurations are provided in see Chapter 3, Setting Up DM-Multipath.Chapter 2. Multipath DevicesChapter 2. Multipath DevicesWithout DM-Multipath, each path from a server node to a s

58、torage controller is treated by the system as a separate device, even when the I/O path connects the same server node to the same storage controller. DM-Multipath provides a way of organizing the I/O paths logically, by creating a single multipath deviceon top of the underlying devices.2.1. Multipath Device IdentifiersEach multipath device has a World Wide Identifier (WWID, which is guaranteed to be globally unique and unchanging. By default, the name of a mult