How to configure device-mapper-multipath - Oracle Solutions - Enterprise Solutions - Dell Community

How to configure device-mapper-multipath

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How to configure device-mapper-multipath

Oracle Solutions

Applies to:
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Enterprise Linux 5.x

Problem
:
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How do I configure device-mapper-multipath?

Solution:
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1. Verify that your device-mapper and multipath driver are at least the version shown below or higher by running the command: rpm -qa | grep device-mapper

device-mapper-1.02.28-2.el5
device-mapper-multipath-0.4.7-23.el5.4.0.1
device-mapper-event-1.02.28-2.el5


2. Identify your local disks i.e. /dev/sda. Once your local disk is determined run the following command to obtain its scsi_id: scsi_id –gus /block/sda

360024e805314c20011faf391033bdece


3. Open the /etc/multipath.conf file and locate and comment out the section below:

#blacklist {
# devnode “*”
#}

4. Once the scsi_id of your local disk has been retrieved, you must blacklist this scsi_id from being used as a multipath device. Within /etc/multipath.conf file and locate, uncomment, and modify the section below:

blacklist {
    wwid <enter your local disk scsi_id here>
    devnode "^(ram|raw|loop|fd|md|dm-|sr|scd|st)[0-9]*"

    devnode "^hd[a-z]"
}


5. Uncomment your defaults section within your /etc/multipath.conf

defaults {
    udev_dir /dev
    polling_interval 10
    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 100
    max_fds 8192
    rr_weight priorities
    failback immediate
    no_path_retry fail
    user_friendly_names yes
}


6. Locate the multipaths section within your /etc/multipath.conf file. In this section you will provide the scsi_id of each iSCSI volume and provide an alias in order to keep a consistent naming convention across all of your OVM Server nodes. An example is shown below:

multipaths {
    multipath {
        wwid <scsi_id of volume1>
        alias alias_of_volume1
    }
    multipath {
        wwid <scsi_id of volume2>
        alias alias_of_volume2
    }
}


NOTE: Additional multipath subsections can be added to meet the number of volumes you need.



7. Restart your multipath daemon service using the following command:

service multipathd restart


8. Verify that your multipath volumes alias are displayed properly by running the following command:
multipath –ll

Alias_of_volume1 (scsi_id of volume1) dm-2 EQLOGIC,100E-00
[size=220G][features=0][hwhandler=0][rw]
\_ round-robin 0 [prio=0][active]
\_ 6:0:0:0 sdaj 66:48 [active][ready]
\_ 4:0:0:0 sdag 66:0 [active][ready]
\_ 3:0:0:0 sdd 8:48 [active][ready]
\_ 5:0:0:0 sdn 8:208 [active][ready]


9. Make sure the iSCSI service starts upon boot using the command:

chkconfig multipathd on

References:
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1. This article is an adaptation of an excerpt from Dell Engineer Roger Lopez's whitepaper on "Best Practices and Performance Characteristics of Running Oracle® RAC 11g with Dell EqualLogic™ on Oracle VM" and can be found here.

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Comments
  • Wes,

    Just wanted to let you know that the information in this article helped me a lot!! Very useful!!

    That's what makes TechCenter great!