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Red Hat DEVICE-MAPPER MULTIPATH 5.2 Configuration And Administration Manual

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Using Device-Mapper Multipath
Configuration and
Administration
5.2
DM_Multipath
ISBN: N/A
Publication date: July 2008

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Summary of Contents for Red Hat DEVICE-MAPPER MULTIPATH 5.2

  • 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 5.2...
  • 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: Bugzilla component: Documentation-cluster Book identifier: DM_Multipath(EN)-5.2 (2008-07-31T15:35)
  • Page 9 Document Conventions /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...

  • 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 In the example shown in Figure 1.2, “Active/Passive Multipath Configuration with Two RAID Devices”, there are two I/O paths to each RAID device (just as there are in the example shown Figure 1.1, “Active/Passive Multipath Configuration with One RAID Device”).

  • Page 14: Storage Array Support

    Chapter 1. Device Mapper Multipathing In this configuration, I/O can be spread among those four paths. 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.

  • Page 15: Dm-Multipath Setup Overview

    DM-Multipath Setup Overview Component Description command Lists and configures multipath devices. Normally started up multipath with , it can also be started up by a /etc/rc.sysinit udev program whenever a block device is added or it can be run by file system.

  • 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...

  • 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. 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 \_ round-robin 0 \_ 0:0:0:0 sda [--------- 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...

  • Page 24: Adding Devices To The Multipathing Database

    Chapter 3. Setting Up DM-Multipath The local disk or disks should no longer be listed in the new multipath maps, as shown in the following example. [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...
  • Page 25 Multipath Devices For more information on the section of the configuration file, see Section 5, devices “Configuration File Devices”.

  • Page 27: 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 28: Configuration File Blacklist

    Chapter 4. The DM-Multipath Configuration File General default settings for DM-Multipath. multipaths Settings for the characteristics of individual multipath devices. These values overwrite what 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.

  • Page 29: Blacklisting By Device Name

    Blacklisting By Device Name entry in the section of the configuration file. blacklist The following example shows the lines in the configuration file that would blacklist a device with a WWID of 26353900f02796769. blacklist { 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...

  • Page 30: Blacklist Exceptions

    Chapter 4. The DM-Multipath Configuration File vendor "IBM" product "3S42" #DS4200 Product 10 device { vendor "HP" product "*" 2.4. Blacklist Exceptions You can use the section of the configuration file to enable multipathing blacklist_exceptions on devices that have been blacklisted by default. For example, by default, devices with vendor = "IBM"...
  • Page 31 Configuration File 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 32 Chapter 4. The DM-Multipath Configuration File Attribute Description = 1 priority group per target node name group_by_node_name The default value is failover getuid_callout Specifies the default program and arguments to call out to obtain a unique path identifier. An absolute path is required. The default value is /sbin/scsi_id -g -u -s Specifies the the default program and arguments to call out to...

  • Page 33: Multipaths Device Configuration Attributes

    Multipaths Device Configuration Attributes Attribute Description A value of indicates that queuing should not stop until queue the path is fixed. The default value is (null). If set to , specifies that the system should using the user_friendly_names bindings file to assign a /var/lib/multipath/bindings persistent and unique alias to the multipath, in the form of...
  • 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. rr_weight If set to , then instead of sending priorities rr_min_io requests to a path before calling...

  • Page 35: Configuration File Devices

    Configuration File Devices 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 configuration file. These attributes are devices multipath.conf used by DM-Multipath unless they are overwritten by the attributes specified in the multipaths section of the...
  • Page 36 Chapter 4. The DM-Multipath Configuration File device for multipath. Attribute Description Specifies the vendor name of the storage device to which the vendor attributes apply, for example device COMPAQ Specifies the product name of the storage device to which the product attributes apply, for example device...
  • Page 37 Configuration File Devices Attribute Description default value is Specifies the number of I/O requests to route to a path before rr_min_io switching to the next path in the current path group. The default value is 1000. rr_weight If set to , then instead of sending priorities rr_min_io...

  • Page 39: 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 40: 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 41: 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 42 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 43: Index

    rr_min_io parameter, 21, 23 Index rr_weight parameter, 21, 23, 26 selector parameter, 21 udev_dir parameter, 21 Symbols user_friendly_names parameter, 20, 21 vendor parameter, 26 /etc/multipath.conf package, 11 wwid parameter, 23 configuring DM-Multipath, 11 active/active configuration definition, 1 illustration, 3 defaults section active/passive configuration multipath.conf file, 20 definition, 1...
  • Page 44 Index getuid_callout parameter, 21, 26 prio_callout parameter, 21, 26 product parameter, 26 product_blacklist parameter, 26 hardware_handler parameter, 26 rr_min_io parameter, 21, 23 rr_weight parameter, 21, 23, 26 kpartx command , 4 selector parameter, 21 local disks, ignoring, 12 setup LVM physical volumes DM-Multipath, 11 multipath devices, 8 storage array support, 4...

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