The multipath configuration file is divided into the following sections:

When the system determines the attributes of a multipath device, first it checks the multipath settings, then the devices settings, then the multipath system defaults.

The recovery_tmo sysfs option controls the timeout for a particular iSCSI device. The following options globally override recovery_tmo values:

The DM Multipath fast_io_fail_tmo option takes precedence over replacement_timeout. Red Hat does not recommend using replacement_timeout to override recovery_tmo in devices managed by DM Multipath because DM Multipath always resets recovery_tmo when the multipathd service reloads.

You can configure DM Multipath to ignore selected devices when it configures multipath devices. DM Multipath does not group these ignored devices into a multipath device.

blacklist {
       devnode "!^(sd[a-z]|dasd[a-z]|nvme[0-9])"
}

The /etc/multipath.conf configuration file includes a defaults section that sets the user_friendly_names parameter to yes, as follows.

defaults {
        user_friendly_names yes
}

This overwrites the default value of the user_friendly_names parameter.

The configuration file includes a template of configuration defaults. This section is commented out, as follows.

#defaults {
#       polling_interval        10
#       path_selector           "round-robin 0"
#       path_grouping_policy    multibus
#       uid_attribute           ID_SERIAL
#       prio                    alua
#       path_checker            readsector0
#       rr_min_io               100
#       max_fds                 8192
#       rr_weight               priorities
#       failback                immediate
#       no_path_retry           fail
#       user_friendly_names     yes
#}

To overwrite the default value for any of the configuration parameters, you can copy the relevant line from this template into the defaults section and uncomment it. For example, to overwrite the path_grouping_policy parameter so that it is multibus rather than the default value of failover, copy the appropriate line from the template to the initial defaults section of the configuration file, and uncomment it, as follows.

defaults {
        user_friendly_names     yes
        path_grouping_policy    multibus
}

For information on the attributes that are set in the defaults section of the multipath.conf configuration file see the multipath.conf(5) man page. These values are used by DM Multipath unless they are overwritten by the attributes specified in the devices, multipaths, or overrides sections of the multipath.conf file.

The attributes in the multipaths section of the multipath.conf configuration file apply only to the one specified multipath. These defaults are used by DM Multipath and override attributes set in the overrides, defaults, and devices sections of the multipath.conf file.

For information on the attributes that are set in the multipaths section of the multipath.conf configuration file see the multipath.conf(5) man page.

The following example shows multipath attributes specified in the configuration file for two specific multipath devices. The first device has a WWID of 3600508b4000156d70001200000b0000 and a symbolic name of yellow.

The second multipath device in the example has a WWID of 1DEC_321816758474 and a symbolic name of red. In this example, the rr_weight attributes is set to priorities.

multipaths {
       multipath {
              wwid                  3600508b4000156d70001200000b0000
              alias                 yellow
              path_grouping_policy  multibus
              path_selector         "round-robin 0"
              failback              manual
              rr_weight             priorities
              no_path_retry         5
       }
       multipath {
              wwid                  1DEC_321816758474
              alias                 red
              rr_weight             priorities
        }
}

The devices section of the multipath.conf configuration file sets attributes for individual storage devices. These attributes are used by DM Multipath unless they are overwritten by the attributes specified in the multipaths or overrides sections of the multipath.conf file for paths that contain the device. These attributes override the attributes set in the defaults section of the multipath.conf file.

For information on the attributes that are set in the devices section of the multipath.conf configuration file see the multipath.conf(5) man page.

Many devices that support multipathing are included by default in a multipath configuration. For information on the default configuration value, including supported devices, run either of the following commands.

# multipathd show config
# multipath -t

You probably will not need to modify the values for these devices, but if you do you can overwrite the default values by including an entry in the configuration file for the device that overwrites those values. You can copy the device configuration defaults for the device that the multipathd show config command displays and override the values that you want to change.

To add a device that is not configured automatically by default to this section of the configuration file, you need to set the vendor and product parameters. You can find these values by looking at /sys/block/device_name/device/vendor and /sys/block/device_name/device/model where device_name is the device to be multipathed, as in the following example:

# cat /sys/block/sda/device/vendor
WINSYS
# cat /sys/block/sda/device/model
SF2372

The additional parameters to specify depend on your specific device. If the device is active/active, you will usually not need to set additional parameters. You may want to set path_grouping_policy to multibus. Other parameters you may need to set are no_path_retry and rr_min_io.

If the device is active/passive, but it automatically switches paths with I/O to the passive path, you need to change the checker function to one that does not send I/O to the path to test if it is working (otherwise, your device will keep failing over). This almost always means that you set the path_checker to tur; this works for all SCSI devices that support the Test Unit Ready command, which most do.

If the device needs a special command to switch paths, then configuring this device for multipath requires a hardware handler kernel module. The current available hardware handler is emc. If this is not sufficient for your device, you may not be able to configure the device for multipath.

The following example shows a device entry in the multipath configuration file.

#	}
#	device {
#		vendor			"COMPAQ  "
#		product			"MSA1000         "
#		path_grouping_policy	multibus
#		path_checker		tur
#		rr_weight		priorities
#	}
#}

The overrides section of the multipath.conf configuration file allows you to set a configuration value for all of your devices. For example, you may want all devices to set no_path_retry to fail. This section supports all of the attributes that are supported by both the devices and defaults section of the multipath.conf configuration file, which is all of the devices section attributes except vendor, product and revision. These attributes are used by DM Multipath for all devices unless they are overwritten by the attributes specified in the multipaths section of the multipath.conf file for paths that contain the device. These attributes override the attributes set in the devices and defaults sections of the multipath.conf file.

For information on the attributes that are set in the devices and defaults sections of the multipath.conf configuration file see the multipath.conf(5) man page.