Chapter 3. Setting Up DM-Multipath

Chapter 3. Setting Up DM-Multipath

3.1. Setting Up DM-Multipath
3.2. Ignoring Local Disks when Generating Multipath Devices
3.3. Adding Devices to the Multipathing Database

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

3.1. Setting Up DM-Multipath

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

Use the following procedure to set up DM-Multipath for a basic failover configuration.

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 "*"
}
```
After commenting out those lines, this section appears as follows.
```
# 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. For information on changing the values in the configuration file to something other than the defaults, see Chapter 4, The DM-Multipath Configuration File.
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.
Execute the following commands:
```
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.
For further information on the multipath command output, see Section 5.4, “Multipath Command Output”.
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. For information on setting the name of the device to an alias of your choosing, see Chapter 4, The DM-Multipath Configuration File.