Chapter 3. Setting Up DM-Multipath
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
- Starting multipath in the
initramfs
file system
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.
You set up multipath with the
mpathconf
utility, which creates the multipath configuration file /etc/multipath.conf
.
- If the
/etc/multipath.conf
file already exists, thempathconf
utility will edit it. - If the
/etc/multipath.conf
file does not exist, thempathconf
utility will use the/usr/share/doc/device-mapper-multipath-0.4.9/multipath.conf
file as the starting file. - If the
/usr/share/doc/device-mapper-multipath-0.4.9/multipath.conf
file does not exist thempathconf
utility will create the/etc/multipath.conf
file from scratch.
If you do not need to edit the
/etc/multipath.conf
file, you can set up DM-Multipath for a basic failover configuration by running the following command. This command enables the multipath configuration file and starts the multipathd
daemon.
# mpathconf --enable --with_multipathd y
If you need to edit the
/etc/multipath.conf
file before starting the multipathd
daemon. use the following procedure to set up DM-Multipath for a basic failover configuration.
- Run the
mpathconf
command with the--enable
option specified:#
mpathconf --enable
For information on additional options to thempathconf
command you may require, see thempathconf
man page or enter thempathconf
command with the--help
option specified.#
mpathconf --help
usage: /sbin/mpathconf <command> Commands: Enable: --enable Disable: --disable Set user_friendly_names (Default n): --user_friendly_names <y|n> Set find_multipaths (Default n): --find_multipaths <y|n> Load the dm-multipath modules on enable (Default y): --with_module <y|n> start/stop/reload multipathd (Default n): --with_multipathd <y|n> chkconfig on/off multipathd (Default y): --with_chkconfig <y|n> - Edit the
/etc/multipath.conf
file if necessary. 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 ofpath_grouping_policy
is set tofailover
, so in this example you do not need to edit the/etc/multipath.conf
file. 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 so that the names of the multipath devices are of the formmpath
n; 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, if necessary.
- Execute the following command:
#
service multipathd start
Since the value of
user_friendly_names
is set to yes
in the configuration file, the multipath devices will be created as /dev/mapper/mpath
n. For information on setting the name of the device to an alias of your choosing, see Chapter 4, The DM-Multipath Configuration File.
If you do not want to use user friendly names, you can enter the following command:
# mpathconf --enable --user_friendly_names n
Note
If you find that you need to edit the multipath configuration file after you have started the multipath daemon, you must execute the
service multipathd reload
command for the changes to take effect.