Multipath configuration on RHEL6

1. Check if you have already installed device-mapper-multipath rpm, if not then install it.

rpm -qa device-mapper-multipath

2. If /etc/multipath.conf file doesn’t exist, then copy it from /usr/share/doc/device-mapper-multipath-*

cp /usr/share/doc/device-mapper-multipath-0.4.9/multipath.conf /etc/multipath.conf

3. Find WWIDs that should be added to multipath configuration.

# scsi_id -g -u /dev/sdb
36001438009b044d90000900000780000

4. Edit the /etc/multipath.conf configuration file

defaults {
        user_friendly_names yes
        path_grouping_policy    failover
}

blacklist {
        wwid "*"
}

blacklist_exceptions {
        wwid "36001438009b044d90000900000780000"
}

multipaths {
        multipath {
                wwid                    "36001438009b044d90000900000780000"
                alias                   asm1
        }
}

5.  Add module to the Linux kernel:

modprobe dm-multipath

6. Start multipath service:

service multipathd start

7. If you have any syntax errors or any parameters that do not work in your Linux version, the following command will show:

multipath -d

8. Commit the configuration:

multipath -v2

9. The following command must find the paths , or you have a bad configuration in multipath.conf file:

multipath -ll

10. Make devices configured after a reboot:

chkconfig multipathd on

If you have made any mistakes in multipath.conf file then correct them and do  the following steps to make changes take affect :

1. edit the /etc/multipath.conf

2.  Reload the multipath service:

service multipathd reload

3.  Remove all unused multipath devices

multipath -F

4.  Check again that syntax is correct:

multipath –d

5.  Commit the changes:

multipath –v2

Note that, this configuration is very simple, but it is working also perfectly.

For more multipath options and more sophisticated configuration, see the following documentation.