Multipath devices use specific naming conventions that determine how they appear in the file system. They can be identified by their World Wide Identifier (WWID) or user-friendly names like mpathN, depending on your configuration preferences.

When new devices are under the control of Device Mapper (DM) Multipath, these devices are created in the /dev/mapper/ and /dev/ directory.

Note

Any devices of the form /dev/dm-X are for internal use only and should never be used by the administrator directly.

The following describes multipath device names:

• When the user_friendly_names configuration option is set to no, the name of the multipath device is set to World Wide Identifier (WWID). By default, the name of a multipath device is set to its WWID. The device name would be /dev/mapper/WWID. It is also created in the /dev/ directory, named as /dev/dm-X.
• Alternately, you can set the user_friendly_names option to yes in the /etc/multipath.conf file. This sets the alias in the multipath section to a node-unique name of the form mpathN. The device name would be /dev/mapper/mpathN and /dev/dm-X. But the device name is not guaranteed to be the same on all nodes using the multipath device. If you set the alias option in the /etc/multipath.conf file, the name is not automatically consistent across all nodes in the cluster.

Note

This should not cause any difficulties if you use LVM to create logical devices from the multipath device. To keep your multipath device names consistent in every node, disable the user_friendly_names option.

For example, a node has two Host Bus Adapters (HBAs). They connect through an unzoned Fibre Channel (FC) switch to a dual-port storage controller. As a result, the node sees four devices. These devices are, /dev/sda, /dev/sdb, /dev/sdc, and /dev/sdd. DM Multipath creates a single device with a unique WWID that reroutes I/O to those four underlying devices per the multipath configuration.

In addition to the user_friendly_names and alias options, a multipath device also has other attributes. You can modify these attributes for a specific multipath device. To do this, create an entry for that device in the multipaths section of the /etc/multipath.conf file.

You can modify attributes for a specific multipath device by adding an entry in the multipaths section of /etc/multipath.conf.

For more information, see:

• multipath(8) and multipath.conf(8) man pages on your system
• /etc/multipath.conf file