How to setup DM-Multipath in Linux server?

DM-Multipath includes compiled-in default settings that are suitable for common multipath configurations.

Setting up DM-multipath is often a simple procedure.

The basic procedure for configuring your system with DM-Multipath is as follows:

1. Install device-mapper-multipath rpm.
 
Before setting up DM-Multipath on your system, ensure that your system has been updated and includes the device-mapper-multipath package.

2. Edit the multipath.conf configuration file:

  Edit the /etc/multipath.conf file by commenting out the following lines at the top of the file. This section of the configuration   file, in its initial state, blacklists all devices. You must comment it out to enable multipathing.
     
       blacklist {
        devnode "*"
}

The default settings for DM-Multipath are compiled in to the system and do not need to be explicitly set in the /etc/multipath.conf file.

The default value of path_grouping_policy is set to failover, so in this example you do not need to change the default value.

The initial defaults section of the configuration file configures your system that the names of the multipath devices are of the  form mpathn; without this setting, the names of the multipath devices would be aliased to the WWID of the device.

Save the configuration file and exit the editor.

3. Start the multipath daemons.

modprobe dm-multipath
service multipathd start
multipath -v2

The multipath -v2 command prints out multipathed paths that show which devices are multipathed. If the command does not print anything out, ensure that all SAN connections are set up properly and the system is multipathed.

4. Execute the following command to ensure sure that the multipath daemon starts on bootup:

    chkconfig multipathd on

Since the value of user_friendly_name is set to yes in the configuration file the multipath devices will be created as /dev/mapper/mpathn