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Red Hat DEVICE-MAPPER MULTIPATH 4.6 Configuration And Administration Manual

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

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Summary of Contents for Red Hat DEVICE-MAPPER MULTIPATH 4.6

  • Page 1 Using Device-Mapper Multipath Configuration and Administration DM_Multipath ISBN: N/A Publication date: July 2008...
  • Page 2 Using Device-Mapper Multipath This book provides information on using the Device-Mapper Multipath feature of Red Hat Enterprise Linux 4.6...
  • Page 3 All other trademarks referenced herein are the property of their respective owners. The GPG fingerprint of the security@redhat.com key is: CA 20 86 86 2B D6 9D FC 65 F6 EC C4 21 91 80 CD DB 42 A6 0E...
  • Page 4 Using Device-Mapper Multipath...

  • Page 5: Table Of Contents

    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.

  • Page 7: Preface

    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.

  • Page 8: 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)-4.6 (2008-07-31T15:20)
  • Page 9 Document Conventions 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.
  • Page 10 Preface Warning A warning indicates potential data loss, as may happen when tuning hardware for maximum performance.

  • 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 Figure 1.1. Active/Passive Multipath Configuration with One RAID Device In 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 possible failure in this configuration: •...
  • Page 13 Overview of DM-Multipath Figure 1.2. Active/Passive Multipath Configuration with Two RAID Devices As in the example shown in Figure 1.1, “Active/Passive Multipath Configuration with One RAID Device”, there are two I/O paths to each 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 DM-Multipath to switch to the alternate I/O path for that device.

  • Page 14: Storage Array Support

    Chapter 1. Device Mapper Multipathing Figure 1.3. Active/Active Multipath Configuration with One RAID Device 2. Storage Array Support By default, DM-Multipath includes support for the most common storage arrays that support DM-Multipath. The supported devices can be found in the file.

  • Page 15: Dm-Multipath Setup Overview

    DM-Multipath Setup Overview Component Description program whenever a block device is added or it can be run by file system. initramfs daemon Monitors paths; as paths fail and come back, it may initiate multipathd path group switches. Provides for interactive changes to multipath devices.

  • Page 17: 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 18: Multipath Device Attributes

    Chapter 2. Multipath Devices multipath device. This should not cause any difficulties if you use LVM to create logical devices from the multipath device, but if you require that your multipath device names be consistent in every node in the cluster you perform one of the following procedures: •...
  • Page 19 Multipath Devices in Logical Volumes filter = [ "r/disk/", "r/sd.*/", "a/.*/" ]...

  • Page 21: 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 1. Setting Up DM-Multipath Before setting up DM-Multipath on your system, ensure that your system has been updated and includes the package.

  • Page 22: Ignoring Local Disks When Generating Multipath Devices

    Chapter 3. Setting Up DM-Multipath 3. Save the configuration file and exit the editor. 4. Execute the following commands: modprobe dm-multipath service multipathd start multipath -v2 command prints out multipathed paths that show which devices are multipath -v2 multipathed. If the command does not print anything out, ensure that all SAN connections are set up properly and the system is multipathed.
  • Page 23 Ignoring Local Disks when Generating device-mapper ioctl cmd 9 failed: Invalid argument 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...

  • Page 24: 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 25: 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 26: Configuration File Blacklist

    Chapter 4. The DM-Multipath Configuration File is specified in the sections of the configuration file. defaults devices devices Settings for the individual storage controllers. These values overwrite what is specified in section of the configuration file. If you are using a storage array that is not defaults supported by default, you may need to create a subsection for your array.

  • Page 27: Blacklisting By Device Name

    Blacklisting By Device Name wwid 26353900f02796769 2.2. Blacklisting By Device Name You can blacklist device types by device name so that they will not be grouped into a multipath device by specifying a entry in the section of the configuration devnode devnode_blacklist file.
  • Page 28 Chapter 4. The DM-Multipath Configuration File out, as follows. #defaults { udev_dir /dev polling_interval selector "round-robin 0" path_grouping_policy multibus getuid_callout "/sbin/scsi_id -g -u -s /block/%n" prio_callout /bin/true path_checker readsector0 rr_min_io rr_weight priorities failback immediate no_path_retry fail 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 section and uncomment it.
  • Page 29 Configuration File Defaults Attribute Description = all valid paths in 1 priority group multibus = 1 priority group per detected serial group_by_serial number = 1 priority group per path priority value group_by_prio = 1 priority group per target node name group_by_node_name The default value is failover...

  • Page 30: Multipaths Device Configuration Attributes

    Chapter 4. The DM-Multipath Configuration File Attribute Description A value of specifies that failback can happen only with manual operator intervention. The default value is manual A numeric value for this attribute specifies the number of no_path_retry times the system should attempt to use a failed path before disabling queueing.
  • Page 31 Multipaths Device Configuration Attributes Attribute Description = 1 priority group per detected serial group_by_serial number = 1 priority group per path priority value group_by_prio = 1 priority group per target node name group_by_node_name Specifies the default algorithm to use in determining what path_selector path to use for the next I/O operation.

  • Page 32: Configuration File Devices

    Chapter 4. The DM-Multipath Configuration File multipaths { multipath { wwid 3600508b4000156d70001200000b0000 alias yellow path_grouping_policy multibus path_checker readsector0 path_selector "round-robin 0" failback manual rr_weight priorities no_path_retry multipath { wwid 1DEC_____321816758474 alias rr_weight priorities 5. Configuration File Devices Table 4.3, “Device Attributes” shows the attributes that you can set for each individual storage device in the section of the...
  • Page 33 Configuration File Devices , as described in Table 4.3, “Device Attributes”. no_path_retry rr_min_io If the device is active/passive, but it automatically switches paths with I/O to the passive path, you need to change the checker function to one that does not send IO/ to the path to test if it is working (otherwise, your device will keep failing over).
  • Page 34 Chapter 4. The DM-Multipath Configuration File Attribute Description A numeric value greater than zero specifies deferred failback, expressed in seconds. A value of specifies that failback can happen only with manual operator intervention. The extra features of multipath devices. The only existing features feature is , which is the same as setting...
  • Page 35 Configuration File Devices path_checker rr_weight priorities...

  • Page 37: 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 38: Multipath Queries With Multipath Command

    Chapter 5. DM-Multipath Administration and Troubleshooting \_ 2:0:0:6 sdb 8:16 [active][ready] \_ round-robin 0 [prio=1][enabled] \_ 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 . If the path is down, ready active the status is...

  • Page 39: Determining Device Mapper Entries With The Dmsetup Command

    Determining Device Mapper Entries with the Option Description Display the current multipath configuration gathered from sysfs and the device mapper. Display the current multipath configuration gathered from sysfs the device mapper, and all other available components on the system. Remove the named multipath device. -f device Remove all multipath devices.
  • Page 40 Chapter 5. DM-Multipath Administration and Troubleshooting enter to get a list of available commands, you can enter a interactive command, or you can help enter to quit. CTRL-D interactive console can be used to troubleshoot problems you may be having multipathd with your system.

  • Page 41: Index

    product parameter, 23 Index rr_min_io parameter, 18, 20 rr_weight parameter, 18, 20, 23 selector parameter, 18 Symbols udev_dir parameter, 18 user_friendly_names parameter, 17, 18 /etc/multipath.conf package, 11 vendor parameter, 23 wwid parameter, 20 configuring active/active configuration DM-Multipath, 11 definition, 1 illustration, 3 active/passive configuration defaults section...
  • Page 42 Index feedback, viii, viii path_selector parameter, 20, 23 polling_interval parameter, 18 prio_callout parameter, 18, 23 product parameter, 23 getuid_callout parameter, 18, 23 rr_min_io parameter, 18, 20 hardware_handler parameter, 23 rr_weight parameter, 18, 20, 23 kpartx command , 4 selector parameter, 18 setup DM-Multipath, 11 local disks, ignoring, 12...

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