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Red Hat ENTERPRISE LINUX 5 DM MULTIPATH Configuration And Administration Manual

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Red Hat Enterprise Linux 5
DM Multipath
DM Multipath Configuration and Administration

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  Summary of Contents for Red Hat ENTERPRISE LINUX 5 DM MULTIPATH

  • Page 1 Red Hat Enterprise Linux 5 DM Multipath DM Multipath Configuration and Administration...
  • Page 2 DM Multipath Red Hat Enterprise Linux 5 DM Multipath DM Multipath Configuration and Administration Edition 3 Copyright © 2009 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 (the latest version of the OPL is presently available at http://www.opencontent.org/openpub/).
  • Page 3: Table Of Contents

    Preface 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. Overview of DM-Multipath ..................... 1 1.2.
  • Page 5 • 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, http:// PDF, and RPM versions on the Red Hat Enterprise Linux Documentation CD and online at www.redhat.com/docs/.
  • Page 6 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:...
  • Page 7 Typographic Conventions 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.
  • Page 8 Preface 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.
  • Page 9 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.
  • Page 11: Device Mapper Multipathing

    Chapter 1. Device Mapper Multipathing Device 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 the I/O paths, creating a new device that consists of the aggregated paths.
  • Page 12 Chapter 1. Device Mapper Multipathing • HBA failure • FC cable failure • SAN switch failure • Array controller port failure With 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 Devices”...
  • Page 13: Storage Array Support

    Storage Array Support In this configuration, I/O can be spread among those four paths. Figure 1.3. Active/Active Multipath Configuration with One RAID Device 1.2. Storage Array Support By default, DM-Multipath includes support for the most common storage arrays that support DM- Multipath.
  • Page 14: Dm-Multipath Setup Overview

    Chapter 1. Device Mapper Multipathing Component Description kpartx command Creates device mapper devices for the partitions on a device It is necessary to use this command for DOS-based partitions with DM- MP. The kpartx is provided in its own package, but the device- mapper-multipath package depends on it.
  • Page 15: Multipath Devices

    Chapter 2. Multipath Devices Without DM-Multipath, each path from a server node to a storage 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 device on top of the underlying devices.
  • Page 16: Multipath Device Attributes

    Chapter 2. Multipath Devices a cluster. For information on the multipaths section of the multipath configuration file, see see Section 4.4, “Multipaths Device Configuration Attributes”. • If you want the system-defined user-friendly names to be consistent across all nodes in the cluster, set up all of the multipath devices on one machine.
  • Page 17: Setting Up Dm-Multipath

    Chapter 3. Setting Up DM-Multipath This chapter provides step-by-step example procedures for configuring DM-Multipath. It includes the following procedures: • Basic DM-Multipath setup • Ignoring local disks • Adding more devices to the configuration file 3.1. Setting Up DM-Multipath Before setting up DM-Multipath on your system, ensure that your system has been updated and includes the device-mapper-multipath package.
  • Page 18: Ignoring Local Disks When Generating Multipath Devices

    Chapter 3. Setting Up DM-Multipath service multipathd start multipath -v2 The multipath -v2 command prints out multipathed paths that show which devices are multipathed. If the command does not print anything out, ensure that all SAN connections are set up properly and the system is multipathed. Section 5.5, “Multipath For further information on the multipath command output, see Command...
  • Page 19 Ignoring Local Disks when Generating Multipath Devices [size=12 GB][features="0"][hwhandler="0"] \_ round-robin 0 \_ 2:0:0:1 sdc 8:32 \_ 3:0:0:1 sdg 8:96 create: 3600a0b80001327d800000070436216b3 [size=12 GB][features="0"][hwhandler="0"] \_ round-robin 0 \_ 2:0:0:2 sdd 8:48 \_ 3:0:0:2 sdh 8:112 create: 3600a0b80001327510000009b4362163e [size=12 GB][features="0"][hwhandler="0"] \_ round-robin 0 \_ 2:0:0:3 sde 8:64 \_ 3:0:0:3 sdi...
  • Page 20: Adding Devices To The Multipathing Database

    Chapter 3. Setting Up DM-Multipath [root@rh4cluster1 ~]# multipath -v2 create: 3600a0b80001327d80000006d43621677 [size=12 GB][features="0"][hwhandler="0"] \_ round-robin 0 \_ 2:0:0:0 sdb 8:16 \_ 3:0:0:0 sdf 8:80 create: 3600a0b80001327510000009a436215ec [size=12 GB][features="0"][hwhandler="0"] \_ round-robin 0 \_ 2:0:0:1 sdc 8:32 \_ 3:0:0:1 sdg 8:96 create: 3600a0b80001327d800000070436216b3 [size=12 GB][features="0"][hwhandler="0"] \_ round-robin 0 \_ 2:0:0:2 sdd...
  • Page 21: The Dm-Multipath Configuration File

    Chapter 4. The DM-Multipath Configuration File By default, DM-Multipath provides configuration values for the most common uses of multipathing. In addition, DM-Multipath includes support for the most common storage arrays that support DM- Multipath. The default configuration values and the supported devices can be found in the /usr/ share/doc/device-mapper-multipath-0.4.7/multipath.conf.defaults file.
  • Page 22: Configuration File Blacklist

    Chapter 4. The DM-Multipath Configuration File devices Settings for the individual storage controllers. These values overwrite what is specified in the defaults section of the configuration file. If you are using a storage array that is not supported by default, you may need to create a devices subsection for your array. When the system determines the attributes of a multipath device, first it checks the multipath settings, then the per devices settings, then the multipath system defaults.
  • Page 23: Blacklisting By Device Type

    Blacklisting By Device Type The following example shows the lines in the configuration file that would blacklist all SCSI devices, since it blacklists are sd* devices. blacklist { devnode "^sd[a-z]" You can use a devnode entry in the blacklist section of the configuraion file to specify individual devices to blacklist rather than all devices of specific type;...
  • Page 24: Configuration File Defaults

    Chapter 4. The DM-Multipath Configuration File blacklist_exceptions { device { vendor "IBM" product "S/390.*" When specifying devices in the blacklist_exceptions section of the configuration file, you must specify the exceptions in the same way they were specified in the blacklist. For example, a WWID exception will not apply to devices specified by a devnode blacklist entry, even if the blacklisted device is associated with that WWID.
  • Page 25 Configuration File Defaults defaults { user_friendly_names path_grouping_policy multibus Table 4.1, “Multipath Configuration Defaults” describes the attributes that are set in the defaults section of the multipath.conf configuration file. These values are used by DM-Multipath unless they are overwritten by the attributes specified in the devices and multipaths sections of the multipath.conf file.
  • Page 26 Chapter 4. The DM-Multipath Configuration File Attribute Description next path, the number of requests to send is determined by rr_min_io times the path's priority, as determined by the prio_callout program. Currently, there are priority callouts only for devices that use the group_by_prio path grouping policy, which means that all the paths in a path group will always have the same priority.
  • Page 27: Multipaths Device Configuration Attributes

    Multipaths Device Configuration Attributes Attribute Description (RHEL 5.3 and later) The group ID to use for the multipath device nodes. You must use the numeric group ID. The default value is determined by the process. Table 4.1. Multipath Configuration Defaults 4.4.
  • Page 28: Configuration File Devices

    Chapter 4. The DM-Multipath Configuration File Attribute Description A value of queue indicates that queuing should not stop until the path is fixed. (RHEL 5.3 and later) If set to yes, the multipathd daemon will flush_on_last_del disable queueing when the last path to a device has been deleted. The default value is no.
  • Page 29 Configuration File Devices multipath.conf file for paths that contain the device. These attributes override the attributes set in the defaults section of the multipath.conf file. Many devices that support multipathing are included by default in a multipath configuration. The values for the devices that are supported by default are listed in the multipath.conf.defaults file.
  • Page 30 Chapter 4. The DM-Multipath Configuration File Attribute Description Specifies the the default program and arguments to call out to prio_callout obtain a path weight. Weights are summed for each path group to determine the next path group to use in case of failue. "none" is a valid value.
  • Page 31 Configuration File Devices Attribute Description (RHEL 5.3 and later) If set to yes, the multipathd daemon will flush_on_last_del disable queueing when the last path to a device has been deleted. The default value is no. Specifies a regular expression used to blacklist devices by product_blacklist product.
  • Page 33: Dm-Multipath Administration And Troubleshooting

    Chapter 5. DM-Multipath Administration and Troubleshooting This chapter will provide information on administering DM-Multipath on a running system. It includes sections on the following topics: • Resizing an Online Multipath Device • The Multipath Daemon • Issues with Large Number of LUNs •...
  • Page 34: The Multipath Daemon

    Chapter 5. DM-Multipath Administration and Troubleshooting For further information on resizing an online LUN, see the Online Storage Reconfiguration Guide. 5.2. The Multipath Daemon If you find you have trouble implementing a multipath configuration, you should ensure that the Chapter 3, Setting Up DM-Multipath.
  • Page 35: Multipath Command Output

    Multipath Command Output 5.5. Multipath Command Output When you create, modify, or list a multipath device, you get a printout of the current device setup. The format is as follows. For each multipath device: action_if_any: alias (wwid_if_different_from_alias) [size][features] [hardware_handler] For each path group: \_ scheduling_policy [path_group_priority_if_known] [path_group_status_if_known] For each path:...
  • Page 36: Multipath Command Options

    Chapter 5. DM-Multipath Administration and Troubleshooting the device mapper. The -ll option displays the information the -l displays in addition to all other available components of the system. When displaying the multipath configuration, there are three verbosity levels you can specify with the -v option of the multipath command.
  • Page 37: Troubleshooting With The Multipathd Interactive Console

    Troubleshooting with the multipathd Interactive Console mpath6p1 (253, 14) mpath7p1 (253, 13) mpath0 (253, 2) mpath7 (253, 9) mpath6 (253, 8) VolGroup00-LogVol01 (253, 1) mpath5 (253, 7) VolGroup00-LogVol00 (253, 0) mpath4 (253, 6) mpath1p1 (253, 10) mpath3 (253, 5) 5.9. Troubleshooting with the multipathd Interactive Console The multipathd -k command is an interactive interface to the multipathd daemon.
  • Page 39: A. Revision History

    Appendix A. Revision History Revision 5.4-1 Tue Aug 18 2009 Steven Levine slevine@redhat.com Resolves: #466970 Adds note clarifying that if a multipathed device contains partitions, you cannot create a logical volume using the whole device without removing the partitions. Resolves #513330 Elaborates documentation to address issues with queue_if_no_path features option.
  • Page 41: Index

    Index product_blacklist parameter, 19 queue_without_daemon parameter, 15 rr_min_io parameter, 15, 17 rr_weight parameter, 15, 17, 19 Symbols selector parameter, 15 /etc/multipath.conf package, 7 udev_dir parameter, 15 uid parameter, 15, 17 user_friendly_names parameter, 14, 15 vendor parameter, 19 active/active configuration wwid parameter, 17 definition, 1 configuring illustration, 2...
  • Page 42 Index gid parameter, 15, 17 product parameter, 19 product_blacklist parameter, 19 hardware_handler parameter, 19 queue_without_daemon parameter, 15 kpartx command , 3 resizing a multipath device, 23 rr_min_io parameter, 15, 17 rr_weight parameter, 15, 17, 19 local disks, ignoring, 8 LVM physical volumes multipath devices, 6 lvm.conf file , 6 selector parameter, 15...