Related Manuals for Red Hat ENTERPRISE LINUX 4 - DM MULTIPATH
Summary of Contents for Red Hat ENTERPRISE LINUX 4 - DM MULTIPATH
- Page 1 Red Hat Enterprise Linux 4 DM Multipath DM Multipath Configuration and Administration...
- Page 2 DM Multipath Red Hat Enterprise Linux 4 DM Multipath DM Multipath Configuration and Administration Edition 1.0 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/).
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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: Preface
• 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... -
Page 6: Feedback
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) - 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.
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Page 8: Pull-Quote Conventions
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.
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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”...
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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 multipath -v2 The multipath -v2 command prints out multipathed paths that show which devices are multipathed, but only for the devices created by this command. If the command does yield any output, you can check your multipath devices as follows: •... - Page 19 Ignoring Local Disks when Generating Multipath Devices device-mapper ioctl cmd 14 failed: No such device or address 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...
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Page 20: Adding Devices To The Multipathing Database
Chapter 3. Setting Up DM-Multipath [root@rh4cluster1 ~]# multipath -F [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"]... -
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-0.4.5/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: Configuration File Defaults
Configuration File Defaults The following example shows the lines in the configuration file that would blacklist all SCSI devices, since it blacklists are sd* devices. devnode_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 Chapter 4. The DM-Multipath Configuration File user_friendly_name To overwrite the default value for any of the configuration parameters, you can copy the relevant line from this template into the defaults section and uncomment it. For example, to overwrite the path_grouping_policy parameter so that it is multibus rather than the default value of failover, copy the appropriate line from the template to the initial defaults section of the configuration file, and uncomment it, as follows.
- Page 25 Configuration File Defaults Attribute Description emc_clariion, hp_sw, and directio. The default value is readsector0. Specifies path group failback. failback A value of 0 or immediate specifies that as soon as there is a path group with a higher priority than the current path group the system switches to that path group.
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Page 26: Multipaths Device Configuration Attributes
Chapter 4. The DM-Multipath Configuration File Attribute Description (RHEL 4.6 and later) The location of the bindings file that is bindings_file used with the user_friendly_names option. The default value is /var/lib/multipath/bindings. (RHEL 4.7 and later) The mode to use for the multipath device mode nodes, in octal. - Page 27 Multipaths Device Configuration Attributes Attribute Description If set to priorities, then instead of sending rr_min_io rr_weight requests to a path before calling selector to choose the 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.
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Page 28: Configuration File Devices
Chapter 4. The DM-Multipath Configuration File wwid 1DEC_____321816758474 alias rr_weight priorities 4.5. Configuration File Devices Table 4.3, “Device Attributes” shows the attributes that you can set for each individual storage device in the devices section of the multipath.conf configuration file. These attributes are used by DM- Multipath unless they are overwritten by the attributes specified in the multipaths section of the multipath.conf file for paths that contain the device. - Page 29 Configuration File Devices Attribute Description Specifies the product name of the storage device to which the product device attributes apply, for example HSV110 (C)COMPAQ. Specifies a regular expression used to blacklist devices by vendor/ bl_product product. Note that for a device to get blacklisted, the vendor, product, and bl_product strings must all match.
- Page 30 Chapter 4. The DM-Multipath Configuration File Attribute Description 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. If set to uniform, all path weights are equal. The default value is uniform.
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Page 31: 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: • Multipath Command Output • Multipath Queries with multipath Command • Multipath Command Options • Multipath Queries with dmsetup Command •... -
Page 32: Multipath Queries With Multipath Command
Chapter 5. DM-Multipath Administration and Troubleshooting \_ 3:0:0:6 sdc 8:64 [active][ready] If the path is up and ready for I/O, the status of the path is ready or active. If the path is down, the status is faulty or failed. The path status is updated periodically by the multipathd daemon based on the polling interval defined in the /etc/multipath.conf file. -
Page 33: Determining Device Mapper Entries With The Dmsetup Command
Determining Device Mapper Entries with the dmsetup Command Option Description Remove the named multipath device. -f device Remove all multipath devices. Table 5.1. Useful multipath Command Options 5.4. Determining Device Mapper Entries with the dmsetup Command You can use the dmsetup command to find out which device mapper entries match the multipathed devices. -
Page 34: Resizing An Online Multipathed Device (Rhel 4.8 And Later)
Chapter 5. DM-Multipath Administration and Troubleshooting > > CTRL-D The following command sequence ensures that multipath has picked up any changes to the multipath.conf, # multipathd -k > > reconfigure > > CTRL-D Use the following command sequence to ensure that the path checker is working properly. # multipathd -k >... - Page 35 Resizing an Online Multipathed Device (RHEL 4.8 and later) dmsetup resume device_name...
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Page 37: Revision History
Appendix A. Revision History Revision 1.0 Wed Apr 01 2009... -
Page 39: Index
Index uid parameter, 14 user_friendly_names parameter, 13, 14 vendor parameter, 18 wwid parameter, 16 configuring active/active configuration DM-Multipath, 7 definition, 1 illustration, 2 active/passive configuration defaults section definition, 1 multipath.conf file, 13 illustration, 1 dev/mapper directory, 5 alias parameter , 16 dev/mpath directory, 5 configuration file, 5 device name, 5... - Page 40 Index rr_weight parameter, 14, 16, 18 hardware_handler parameter, 18 selector parameter, 14 setup kpartx command , 3 DM-Multipath, 7 storage array support, 3 storage arrays local disks, ignoring, 8 adding, 10, 18 LVM physical volumes multipath devices, 6 lvm.conf file , 6 udev_dir parameter, 14 uid parameter, 14 user_friendly_names parameter , 5, 13, 14...