Per default the multipath system will create a dm-X device (where X is a number) as a single device that reroutes I/O to the underlying disks. If you set the user_friendly_names option in the /etc/multipath.conf file an alias is created as /dev/mapper/mpathN (where N is a number). The /dev/dm-X device should never be used since it is as volatile as the other device names. The name is handed out on a first come first serve manner and can thus change after a reboot. The /dev/mapper/mpath-N device is bound to the WWID of the multipath device and is stable over reboots. Use this name to configure and setup your multipath system.

The mapping between the WWID and the user friendly names is maintained in the /var/lib/multipath/bindings file. If you want your bindings to be identical on all your hosts distribute this file to all your systems. You can even set the bindings_file option in /etc/multipath.conf if you want this file to be placed in a different place then the default one e.g. /etc/multipath.d/bindings. Another, and probably more flexible, option to have identical names across your nodes is by only using the WWID named devices in /dev/disk/by-id/. Or use aliases.

We start our configuration file with some defaults. The provided values are the default values for these options, so nothing fancy. This section is only provided to give you an idea of how it works. For more details use man 5 multipath.conf:

defaults {
        udev_dir		/dev
        user_friendly_names	yes
}

To prevent multipath from using devices that do not have a multipath we start the configuration file with a line that will blacklist all devices from multipathing:

blacklist {
	devnode "^(ram|raw|loop|fd|md|dm-|sr|scd|st)[0-9]*"
	devnode "^hd[a-z]"
}

I tried a setup of devnode "*" and then enabling a vendor and product device in the blacklist_exceptions section, but that doesn't seem to work. So for now we blacklist everything this is an unlikely multipath candidate. Although the other setup should work...
After this section we can start to exclude certain devices or nodes from the blacklist if needed:

blacklist_exceptions {
}

The Dell devices are standard supported devices by multipathd, so there is not much we need to do in the following section, but we can use it to override the default settings if we want to. The devices section can also be used to define devices that are not per default supported by multipath, more on this later in this chapter. Options set in the device section override the once in the defaults section.

devices {
	# device-specific settings
	# Can only contain one or more device{} subsections
}

The multipaths section can only contain subsections called multipath. These sections can be used to define aliases for easy reading, and multipath specific options. The following is a simple example that will create a device /dev/mapper/mp-home device. Options set in the multipath section override options set in previous sections.

multipaths {
	# multipath topologies
	# Can only contain one or more multipath{} subsections
	multipath {
		wwid 36a4badb00018e1c50000051c4c450a6b
		alias mp-home
	}
}