Chapter 5. Modifying the DM Multipath configuration file

By default, DM Multipath provides configuration values for the most common uses of multipathing. In addition, DM Multipath includes support for the most common storage arrays that themselves support DM Multipath.

You can override the default configuration values for DM Multipath by editing the /etc/multipath.conf configuration file. If necessary, you can also add an unsupported by default storage array to the configuration file. In the multipath configuration file, you need to specify only the sections that you need for your configuration, or that you need to change from the default values. If there are sections of the file that are not relevant to your environment or for which you do not need to override the default values, you can leave them commented out, as they are in the initial file.

In the configuration file, you can also use the regular expression.

Note

If you run multipath from the initramfs file system and you make any changes to the multipath configuration files, you must rebuild the initramfs file system for the changes to take effect

5.1. Configuration file overview

The multipath configuration file is divided into the following sections:

blacklist: Listing of specific devices that will not be considered for multipath.
blacklist_exceptions: Listing of multipath devices that would otherwise be ignored according to the parameters of the blacklist section.
defaults: General default settings for DM Multipath.
multipaths: Settings for the characteristics of individual multipath devices. These values overwrite what is specified in the overrides, devices, and defaults sections of the configuration file.
devices: Settings for the individual storage controllers. These values overwrite what is specified in the defaults section of the configuration file. If you are using a storage array that is not supported by default, you may need to create a devices subsection for your array.
overrides: Settings that are applied to all devices. These values overwrite what is specified in the devices and defaults sections of the configuration file.

When the system determines the attributes of a multipath device, it checks the settings of the separate sections from the multipath.conf file in the following order:

multipaths section
overrides section
devices section
defaults section

The following are the ways to view the default configurations:

If you install your machine on a multipath device, the default multipath configuration applies automatically. The default configuration includes the following:
- For a complete list of the default configuration values, execute either multipath -t or multipathd show config command.
- For a list of configuration options with descriptions, see the multipath.conf man page on your system.
If you did not set up multipathing during installation, execute the mpathconf --enable command to get the default configuration.

5.2. Configuration file defaults

The /etc/multipath.conf configuration file contains a defaults section. This section includes the default configuration of Device Mapper (DM) Multipath. The default values might differ based on your initial device settings.

The following table describes the optional attributes, set in the defaults section of the multipath.conf configuration file. If you do not set them, default values from the overrides, or devices sections apply.

Table 5.1. Multipath configuration defaults
Attribute	Description
`polling_interval`	Specifies the interval between two path checks in seconds. For properly functioning paths, the interval between checks gradually increases to `max_polling_interval`. The default value is `5`.
`max_polling_interval`	Specifies the maximum length of the interval between two path checks in seconds.
`max_polling_interval`	The default value is `4 * polling_interval`.
`find_multipaths`	Defines the mode for setting up multipath devices. Available values include:
	`no`: If `find_multipaths` is set to `no`, `multipath` applies rules as with the `strict` value and the `multipathd` daemon applies rules as with the `greedy` value.
	`yes`: If there are at least two devices that are not on the `blacklist` with the same World Wide Identifier (WWID), or if multipath created a multipath device with a device WWID before (even if that multipath device is no longer present), then the device is treated as a multipath device path.
	`greedy`: Both `multipathd` and `multipath` treat every non-blacklisted device as a multipath device path.
	`smart`: Multipath automatically considers that every non-blacklisted device is a multipath device path. If a second path, with the same WWID does not appear within the time set for `find_multipaths_timeout`, multipath releases the device and enables it for use by the rest of the system. The `multipathd` daemon applies rules as with the `yes` value.
	`strict`: This value only treats a device as a multipath path, if you create a multipath device with the device WWID.
	The default value is `off`. The default `multipath.conf` file sets `find_multipaths` to `yes`.
`find_multipaths_timeout`	This represents the timeout in seconds, to wait for additional paths after detecting the first one, if `find_multipaths` `smart` is set. Possible values include:
	Positive value: If set with a positive value, the timeout applies for all non-blacklisted devices.
	Negative value: If set with a negative value, the timeout applies only to known devices that have an entry in the multipath hardware table, either in the built-in table, or in a `device` section. Other unknown devices use a timeout of only 1 second to avoid booting delays.
	`0`: The system applies the built-in default for this attribute.
	The default value for known hardware is `-10`. This means that known devices have a 10 second timeout. Unknown devices have a 1 second timeout. If the `find_multipaths` attribute has a value other than `smart`, this attribute has no effect.
`uxsock_timeout`	Set the timeout of `multipathd` interactive commands in milliseconds.
	For systems with a large number of devices, `multipathd` interactive commands might timeout and fail. If this happens, increase this timeout to resolve the issue.
	The default value is `4000`.
`reassign_maps`	Enable reassigning of device-mapper maps. With this option, the `multipathd` daemon remaps existing device-mapper maps to always point to the multipath device, not the underlying block devices. Possible values are `yes` and `no`. The default value is `no`.
`verbosity`	The default verbosity value is `2`. Higher values increase the verbosity level. Valid levels are between `0` and `4`.
`path_selector`	Specifies the default algorithm to use in determining what path to use for the next I/O operation. Possible values include:
	`round-robin 0`: Loop through every path in the path group, sending the same number of I/O requests, determined by `rr_min_io` or `rr_min_io_rq`, to each.
	`queue-length 0`: Send the next group of I/O requests down the path with the least number of outstanding I/O requests.
	`service-time 0`: Send the next group of I/O requests down the path with the shortest estimated service time. This is determined by dividing the total size of the outstanding I/O to each path by the relative throughput.
	The default value is `service-time 0`.
`path_grouping_policy`	Specifies the default path grouping policy to apply to unspecified multipaths. Possible values include:
	`failover`: 1 path per priority group.
	`multibus`: All valid paths in 1 priority group.
	`group_by_serial`: 1 priority group per detected serial number.
	`group_by_prio`: 1 priority group per path priority value. Priorities are determined by the `prio` attribute.
	`group_by_node_name`: 1 priority group per target node name. The `/sys/class/fc_transport/target*/node_name` directory includes target node names.
	The default value is `failover`.
`uid_attrs`	Set this option to activate merging `uevents` by WWID. This action might improve uevent processing efficiency. It is also an alternative method to configure the udev properties to use for determining unique path identifiers (WWIDs).
	The value of this option is a space separated list of records like `type:ATTR`, where `type` is matched against the beginning of the device node name, and `ATTR` is the name of the udev property to use for matching devices.
	If you configure this option and it matches the device node name of a device, it overrides any other configured methods for determining the WWID for this device.
	You can enable `uevent` merging by setting this value to `sd:ID_SERIAL dasd:ID_UID nvme:ID_WWN`.
	The default is `unset`.
`prio`	Specifies the default function to call to obtain a path priority value. For example, the ALUA bits in SPC-3 provide an exploitable `prio` value. Possible values include:
	`const`: Set a priority of 1 to all paths.
	`emc`: Generate the path priority for EMC arrays.
	`sysfs`: Generate the path priority from `sysfs`. This prioritizer accepts the optional `prio_arg` value `exclusive_pref_bit`. The `sysfs` value uses the `sysfs` attributes `access_state` and `preferred_path`.
	`alua`: Generate the path priority based on the SCSI-3 ALUA settings. If you specify `prio alua` and `prio_args` `exclusive_pref_bit` in your device configuration, multipath creates a path group that contains only the path with the `exclusive_pref_bit` set, and assigns that path group the highest priority. Refer to the `multipath.conf(5)` man page for more information about this type of cases.
	`ontap`: Generate the path priority for NetApp arrays.
	`rdac`: Generate the path priority for LSI/Engenio RDAC controller.
	`hp_sw`: Generate the path priority for Compaq/HP controller in active/standby mode.
	`hds`: Generate the path priority for Hitachi HDS Modular storage arrays.
	`random`: Generate a random priority between 1 and 10.
	`weightedpath`: Generate the path priority based on the regular expression and the provided priority as an argument. Requires a `prio_args` keyword.
	`path_latency`: Generate the path priority based on a latency algorithm. Requires a `prio_args` keyword.
	`ana`: Generate the path priority based on the NVMe ANA settings. This priority routine is hardware dependent.
	`datacore`: Generate the path priority for some DataCore storage arrays. Requires a `prio_args` keyword. This priority routine is hardware dependent.
	`iet`: Generate path priority for iSCSI targets based on IP their address. Requires a `prio_args` keyword. This priority routine is available only with iSCSI.
	The default value depends on the `detect_prio` setting. If `detect_prio` is set to `yes`, then the default priority algorithm is `sysfs`. The only exception is for NetAPP E-Series, where the default is `alua`. If `detect_prio` is set to `no`, the default priority algorithm is `const`.
`prio_args`	Arguments to pass to the `prio` function. This applies only to the following prioritizers:
	`weighted`: Needs a value of the form `<hbtl,devname,serial,wwn> <regex1> <prio1> <regex2> <prio2>`
	`hbtl`: The Regex value can be of SCSI H:B:T:L format. For example: `1:0:.:. , *:0:0:`.
	`devname`: The Regex value can be in device name format. For example: `sda`, `sd.e`.
	`serial`: The Regex value can be in serial number format. Look up `serial` through `sysfs`, or by running the command `multipathd show paths format "%z"`.
	`wwn`: The Regex value can be in the form `host_wwnn:host_wwpn:target_wwnn:target_wwpn`. These values can be looked up through `sysfs` or by running the command `multipathd show paths format %N:%R:%n:%r"`.
	`path_latency`: Requires a value in the form `io_num= <integer> base_num=<integer>`.
	`io_num`: The number of read IOs, continuously sent to the current path. This value helps calculate the average path latency. Valid values include `Integer`, `[2, 200]`.
	`base_num`: The base number value of logarithmic scale. This value helps to partition different priority ranks. Valid values include `Integer`, `[2, 10]`. The maximum average latency value is `100s` and the minimum average latency value is `1us`.
	`alua`: If the `exclusive_pref_bit` value is set, paths with the `preferred_path_bit` set always create their own path group.
	`sysfs`: If the `exclusive_pref_bit` value is set, paths with the `preferred_path_bit` set always create their own path group.
	`datacore`: Requires a value of the form `timeout=<milliseconds> preferredsds=<name>`.
	`preferredsds`: This value is mandatory and it represents the preferred SDS name.
	`timeout`: This value is optional. Set the timeout for the inquiry in milliseconds.
	`iet`: Requires a value of the form `preferredip=<ip_address>`.
	`preferredip`: This value is mandatory. This is the preferred IP address, in dotted decimal notation, for iSCSI targets.
	The default value is `unset`.
`features`	The default extra features of multipath devices, using the format: "number_of_features_plus_arguments feature1 …".
	Possible values for `features` include:
	`queue_if_no_path`: The same as setting `no_path_retry` to `queue`.
	`pg_init_retries n`: Retry path group initialization up to n times before failing. The number must be between 1 and 50.
	`pg_init_delay_msecs msecs`: Number of milliseconds before `pg_init` retry initiates. The number must be between 0 and 60000.
	`queue_mode mode`: Select the queueing mode per multipath device. The mode value options are `bio`, `rq` or `mq`. These correspond to bio-based, request-based, and block-multiqueue request-based (`blk-mq`), respectively.
	By default, the value is unset.
`path_checker`	Specifies the default method to determine the state of the paths. Possible values include:
	`readsector0`: Read the first sector of the device.
	`tur`: Issue a `TEST UNIT READY` command to the device.
	`emc_clariion`: Query the EMC Clariion specific EVPD page 0xC0 to determine the path.
	`hp_sw`: Check the path state for HP storage arrays with Active/Standby firmware.
	`rdac`: Check the path state for LSI/Engenio RDAC storage controller.
	`directio`: Read the first sector with direct I/O.
	`cciss_tur`: Check the path state for HP/COMPAQ Smart Array(CCISS) controllers. This is hardware dependent.
	`none`: Does not check the device. Falls back to use values retrieved from `sysfs`.
	The default value is `tur`.
`alias_prefix`	This attribute represents the `user_friendly_names` prefix.
`alias_prefix`	The default value is `mpath`.
`failback`	Manages path group failback. Possible values include:
	`immediate`: Specifies immediate failback to the highest priority path group that contains active paths.
	`manual`: Specifies that there is no immediate failback, but that failback can happen only with operator intervention.
	`followover`: Specifies that automatic failback can only be performed when the first path of a path group becomes active. This keeps a node from automatically failing back, when another node requested the failover.
	A numeric value greater than zero, specifies deferred failback, and is expressed in seconds.
	The default value is `manual`.
`rr_min_io`	Specifies the number of I/O requests to route to a path before switching to the next path in the current path group. This setting is only for systems running kernels older than 2.6.31. Newer systems should use `rr_min_io_rq`. The default value is `1000`.
`rr_min_io_rq`	Specifies the number of I/O requests to route to a path, before switching to the next path in the current path group. Uses a request-based device-mapper-multipath. This setting can be used on systems running current kernels. On systems running kernels older than 2.6.31, use `rr_min_io`. The default value is `1`.
`no_path_retry`	A numeric value for this attribute specifies the number of times that the path checker must fail for all paths in a multipath device, before disabling queuing.
	A value of `fail` indicates immediate failure, without queuing.
	A value of `queue` indicates that queuing should not stop until the path is fixed.
	The default value is `fail`.
`user_friendly_names`	Possible values include:
	`yes`: Specifies that the system can use the `/etc/multipath/bindings` file to assign a persistent and unique alias to the multipath, in the form of `mpath<n>`.
	`no`: The system uses the WWID as the alias for the multipath. Any device-specific alias you set in the `multipaths` section of the configuration file, overrides this name.
	The default value is `no`.
`queue_without_daemon`	If set to `no`, the `multipathd` daemon disables queuing for all devices, when it is shut down. The default value is `no`.
`flush_on_last_del`	If set to `yes`, the `multipathd` daemon disables queuing when the last path to a device is deleted. The default value is no.
`max_fds`	Sets the maximum number of open file descriptors that can be opened by multipath and the `multipathd` daemon. This is equivalent to the `ulimit -n` command. The default value is `max`, which sets this to the system limit from `/proc/sys/fs/nr_open`.
`checker_timeout`	The timeout to use for prioritizers and path checkers that issue SCSI commands with an explicit timeout, in seconds. The `sys/block/sd<x>/device/timeout` directory contains the default value.
`fast_io_fail_tmo`	The number of seconds the SCSI layer waits after a problem is detected on an FC remote port, before failing I/O to devices on that remote port. This value must be smaller than the value of `dev_loss_tmo`. Setting this to `off` disables the timeout. The default value is `5`. The `fast_io_fail_tmo` option overrides the values of the `recovery_tmo` and `replacement_timeout` options of the underlying path devices.
`dev_loss_tmo`	The number of seconds the SCSI layer waits after a problem is detected on an FC remote port, before removing it from the system. Setting this to infinity will set this to 2147483647 seconds, or 68 years. The OS determines the default value.
`eh_deadline`	Specifies the maximum number of seconds the SCSI layer spends performing error handling, when SCSI devices fail. After this timeout, the scsi layer performs a full HBA reset. Setting this is necessary in cases where the `rport` is never lost, so `fast_io_fail_tmo` and `dev_loss_tmo` never trigger, but `scsi` commands still hang. When the SCSI error handler performs the HBA reset, this affects all target paths on that HBA. The `eh_deadline` value should only be set in cases where all targets on the affected HBAs are multipathed.
`eh_deadline`	The default value is `unset`.
`detect_prio`	If this is set to `yes`, multipath detects if the device is a SCSI device that supports Asymmetric Logical Unit Access (ALUA), or a NVMe device that supports Asymmetric Namespace Access (ANA). If the device supports ALUA, multipath automatically assigns it the `alua` prioritizer. If the device supports ANA, multipath automatically assigns it the `ana` prioritizer.
	If `detect_prio` is set to `no`, or if the device does not support ALUA or ANA, the `prio` attribute sets the prioritizer.
	The default value is `yes`.
`uid_attribute`	Specifies the `udev` attribute to use for the device WWID.
`uid_attribute`	The default value is device dependent: `ID_SERIAL` for SCSI devices, `ID_UID` for DASD devices, and `ID_WWN` for NVMe devices.
`force_sync`	If set to `yes`, this parameter prevents path checkers from running in async mode. This means that only one checker runs at a time. This is useful in cases where many `multipathd` checkers run in parallel, and can cause significant CPU pressure.
`force_sync`	The default value is `no`.
`strict_timing`	If set to `yes`, the `multipathd` daemon starts a new path checker loop after exactly one second, so that each path check occurs at the exactly set seconds for `polling_interval`. On busy systems, path checks might take longer than one second. The missing ticks are accounted for in the next round. A warning prints if path checks take longer than the set seconds for `polling_interval`.
`strict_timing`	The default value is `no`.
`retrigger_tries`, `retrigger_delay`	Use the `retrigger_tries` and `retrigger_delay` parameters in conjunction to make `multipathd` retrigger uevents. If `udev` fails to completely process the original `uevents`, this leaves multipath unable to use the device. The `retrigger_tries` parameter sets the number of times that multipath tries to retrigger a `uevent`, in case a device is not completely set up. The `retrigger_delay` parameter sets the number of seconds between retries. Both of these options accept numbers greater than or equal to `0`. Setting the `retrigger_tries` parameter to `0` disables retries. Setting the `retrigger_delay` parameter to `0` causes the `uevent` to be reissued on the next loop of the path checker.
`retrigger_tries`, `retrigger_delay`	The default value of `retrigger_tries` is `3`. The default value of `retrigger_delay` is 10.
`missing_uev_wait_timeout`	This attribute controls the number of seconds the `multipathd` daemon waits to receive a change event from `udev` for a newly created multipath device. After that it automatically enables device reloads. In most cases, `multipathd` delays reloads on a device, until it receives a change `uevent` from the initial table load.
`missing_uev_wait_timeout`	The default value is `30`.
`deferred_remove`	If set to `yes`, `multipathd` performs a deferred remove, instead of a regular remove, when the last path device is deleted. This ensures that if a multipathed device is in use when a regular remove is performed and the remove fails, the device is automatically removed, when the last user closes the device. The default value is `no`.
`san_path_err_threshold`, `san_path_err_forget_rate`, `san_path_err_recovery_time`	If you set all three of these attributes to integers greater than zero, they enable the `multipathd` daemon to keep shaky paths from reinstating, by monitoring how frequently the path checker fails. If a path checker fails a path more than the value in the `san_path_err_threshold` attribute, within `san_path_err_forget_rate` checks, then the `multipathd` daemon does not reinstate the path until the value of the `san_path_err_recovery_time` attribute in seconds passes, without any path checker failures.
	See the Shaky paths detection section of the `multipath.conf(5)` for more information.
	The default value is `no`.
`marginal_path_double_failed_time`, `marginal_path_err_sample_time`, `marginal_path_err_rate_threshold`, `marginal_path_err_recheck_gap_time`	If `marginal_path_double_failed_time`, `marginal_path_err_rate_threshold`, and `marginal_path_err_recheck_gap_time` are set to integers greater than `0` and `marginal_path_err_sample_time` is set to an integer greater than `120`, they enable the `multipathd` daemon to keep shaky paths from reinstating, by testing the I/O failure rate of paths that repeatedly fail.
	If a path fails twice within the value set in the `marginal_path_double_failed_time` attribute in seconds, the `multipathd` daemon does not immediately reinstate it, when the path checker determines that it is back up. Instead, `multipathd` issues a steady stream of read I/Os to the path for the value set in the `marginal_path_err_sample_time` attribute in seconds. If there are more than the value set in the `marginal_path_err_rate_threshold` attribute number of errors per thousand I/Os, `multipathd` waits for `marginal_path_err_recheck_gap_time` seconds, and then starts another cycle of testing the path with read I/Os. Otherwise, `multipathd` reinstates the path.
	See the Shaky paths detection section of the `multipath.conf(5)` for more information.
	The default value is `no`.
`marginal_pathgroups`	Possible values include:
	`on`: When one of the marginal path detecting methods determines that a path is marginal, the system reinstates the path and places it in a separate pathgroup. This group comes into effect only after all the non-marginal path groups are tried first. This prevents the possibility of IO errors occurring while the system can still use some marginal paths. The path returns to a regular path group as soon as it passes monitoring for a configured time.
	`off`: The `delay__checks`, `marginal_path_`, and `san_path_err_` attributes keep the system from reinstating any marginal, or shaky* paths, until they are monitored for a configured time.
	`fpin`: The `multipathd` daemon receives `fpin` notifications, sets path states to `marginal`, and regroups paths, as described for the `on` value.
	The `marginal_path_` and `san_path_err_` attributes are implicitly set to `no`.
	See the Shaky paths detection section of the `multipath.conf(5)` for more information.
	The default value is `no`.
`log_checker_err`	If set to `once`, `multipathd` logs the first path checker error at verbosity level 2. The system logs any further errors at verbosity level 3, until the device is restored. If the `log_checker_err` parameter is set to `always`, `multipathd` always logs the path checker error at verbosity level 2. The default value is `always`.
`skip_kpartx`	If set to `yes`, `kpartx` does not automatically create partitions on the device. This enables you to create a multipath device, without creating partitions, even if the device has a partition table. The default value of this option is `no`.
`max_sectors_kb`	Using this option, you can set the `max_sectors_kb` device queue parameter to the specified value on all underlying paths of a multipath device, before the first activation of a multipath device. Whenever the system creates a new multipath device, the device inherits the `max_sectors_kb` value from the path devices. Manually raising this value for the multipath device, or lowering this value for the path devices, can cause multipath to create I/O operations larger than the path devices allow. Using the `max_sectors_kb` parameter is an easy way to set these values, before the creation of a multipath device on top of the path devices, and prevent passing any invalid-sized I/O operations. If you do not set this parameter, the path devices driver sets it automatically, and the multipath device inherits it from the path devices.
`ghost_delay`	This attribute sets the number of seconds that multipath waits after creating a device with only ghost paths, before marking it ready for use in `systemd`. This gives the active paths time to appear before the multipath runs the hardware handler to switch the ghost paths to active ones.
	Setting this to `0` or `no` makes multipath immediately mark a device with only ghost paths as ready.
	The default value is `no`.
`enable_foreign`	This attribute enables or disables foreign libraries.
	The value is a regular expression. Foreign libraries are loaded if their name matches the expression.
	By default, no foreign libraries are enabled. Use `nvme` to enable NVMe native multipath support, or `“.*”` to enable all foreign libraries.
`recheck_wwid`	If set to `yes`, when a failed path is restored, the `multipathd` daemon rechecks the path WWID. If there is a change in the WWID, the path is removed from the current multipath device, and added again as a new path. The `multipathd` daemon also checks the path WWID again if it is manually re-added.
	This option only works for SCSI devices with configuration to use the default `uid_attribute`, `ID_SERIAL`, or `sysfs`, for getting their WWID.
	The default value is `no`.
`remove_retries`	This option sets the number of times multipath retries removing a device that is in use. Between each attempt, multipath becomes inactive for 1 second. The default value is `0`, which means that multipath does not retry the remove.
`detect_checker`	If set to `yes`, multipath checks if the device supports ALUA or Redundant Disk Array Controller (RDAC). If the device supports ALUA, multipath assigns it the `tur` `path_checker`. If the device supports RDAC, the `multipathd` daemon assigns it the `rdac` `path_checker`. If the device does not support ALUA or RDAC, or the `detect_checker` is set to `no`, the `path_checker` attribute sets the path checker.
`detect_checker`	The default value is `yes`.
`reservation_key`	The `mpathpersist` parameter uses this service action reservation key. It must be set for all multipath devices using persistent reservations, and it must be the same as the `RESERVATION KEY` field of the `PERSISTENT RESERVE OUT` parameter list, which contains an 8-byte value provided by the application client to the device server to identify the I_T nexus. If you use the `--param-aptpl` option when registering the key with `mpathpersist`, you must append `:aptpl` to the end of the reservation key.
`reservation_key`	This parameter can also be set to `file`, which causes `mpathpersist` to automatically store the `RESERVATION KEY` used to register the multipath device in the `prkeys` file. The `multipathd` daemon then uses this key to register additional paths as they appear. When you remove the registration, this automatically removes the `RESERVATION KEY` from the `prkeys` file. It is `unset` by default. If persistent reservations are necessary, it is recommended to set this attribute to `file`.
`all_tg_pt`	If this option is set to `yes` when `mpathpersist` registers keys, it treats a registered key from one host to one target port, as going from one host to all target ports. This must be set to `yes` to successfully use `mpathpersist` on arrays that automatically set and clear registration keys on all target ports from a host, instead of per target port per host. The default value is `no`.
`auto_resize`	Controls when the `multipathd` command can automatically resize a multipath device. Possible values include:
	`never`: `multipathd` works without any change. This is the default value.
	`grow_only`: `multipathd` automatically resizes the multipath device when the device’s paths have grown in size.
	`grow_shrink`: `multipathd` automatically resizes the multipath device when the device’s paths have either decreased or grown in size.

Additional resources

multipath.conf(5) man page on your system

5.3. Modifying multipath configuration file defaults

The default values that are set in the defaults section on the multipath.conf file, are used by DM Multipath unless they are overwritten by the attributes specified in the devices, multipath, or overrides sections of the multipath.conf file.

Procedure

View the /etc/multipath.conf configuration file, which includes a template of configuration defaults:

#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
#}

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 to multibus instead of 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
}
```
Validate the /etc/multipath.conf file after modifying the multipath configuration file by running one of the following commands:
- To display any configuration errors, run:
```
# multipath -t > /dev/null
```
- To display the new configuration with the changes added, run:
```
# multipath -t
```
Reload the /etc/multipath.conf file and reconfigure the multipathd daemon for changes to take effect:
```
# service multipathd reload
```

Additional resources

multipath.conf(5) and multipathd(8) man pages on your system

5.4. Configuration file multipaths section

Set attributes of individual multipath devices by using the multipaths section of the /etc/multipath.conf configuration file. Device Mapper (DM) Multipath uses these attributes to override all other configuration settings, including those from the overrides section.

The multipaths section recognizes only the multipath subsection as an attribute. The following table shows the attributes that you can set in the multipath subsection, for each specific multipath device. These attributes apply only to one specified multipath. If several multipath subsections match a specific device World Wide Identifier (WWID), the contents of those subsections merge. The settings from latest entries have priority over any previous versions.

Table 5.2. Multipath subsection attributes
Attribute	Description
`wwid`	Specifies the WWID of the multipath device, to which the multipath attributes apply. This parameter is mandatory for this section of the `multipath.conf` file.
`alias`	Specifies the symbolic name for the multipath device, to which the multipath attributes apply. If you are using `user_friendly_names`, do not set this value to `mpath <n>`. This might cause conflicts with an automatically assigned user friendly name, and give you incorrect device node names.

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.

Example 5.1. Multipath attributes specification

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

Additional resources

multipath.conf(5) man page on your system
Configuration file defaults
Configuration file overrides section

5.5. Configuration file devices section

Use the devices section of the multipath.conf configuration file to define settings for individual storage controller types. Values set in this section overwrite specified values in the defaults section.

The system identifies the storage controller types by the vendor, product, and revision keywords. These keywords are regular expressions and must match the sysfs information about the specific device.

The devices section recognizes only the device subsection as an attribute. If there are multiple keyword matches for a device, the attributes of all matching entries apply to it. If an attribute is specified in several matching device subsections, later versions of entries have priority over any previous entries.

Important

Configuration attributes in the latest version of the device subsections override attributes in any previous devices subsections and from the defaults section.

The following table shows the attributes that you can set in the device subsection.

Table 5.3. Devices section attributes
Attribute	Description
`vendor`	Specifies the regular expression to match the device vendor name. This is a mandatory attribute.
`product`	Specifies the regular expression to match the device product name. This is a mandatory attribute.
`revision`	Specifies the regular expression to match the device product revision. If the revision attribute is missing, all device revisions match.
`product_blacklist`	Multipath uses this attribute to create a device `blacklist` entry that has a `vendor` attribute that matches the `vendor` attribute of this device entry, and a `product` attribute that matches this `product_blacklist` attribute.
`vpd_vendor`	Shows the vendor specific Vital Product Data (VPD) page information, using the VPD page abbreviation.
`vpd_vendor`	The `multipathd` daemon uses this information to gather device specific information. Currently only the `hp3par` VPD page is supported.
`hardware_handler`	Specifies the hardware handler to use for a particular device type. All possible values are hardware dependent and include:
	`emc`: Hardware handler for DGC class arrays, as CLARiiON CX/AX and EMC VNX and Unity families.
	`rdac`: Hardware handler for LSI/Engenio/NetApp RDAC class, as NetApp SANtricity E/EF Series, and OEM arrays from IBM DELL SGI STK and SUN.
	`hp_sw`: Hardware handler for HP/COMPAQ/DEC HSG80 and MSA/HSV arrays with Active/Standby mode exclusively.
	`alua`: Hardware handler for SCSI-3 ALUA compatible arrays.
	`ana`: Hardware handler for NVMe ANA compatible arrays.
	The default value is `unset`.

Important

Linux kernels, versions 4.3 and newer, automatically attach a device handler to known devices. This includes all devices supporting SCSI-3 ALUA). The kernel does not enable changing the handler later on. Setting the hardware_handler attribute for such devices on these kernels takes no effect.

Additional resources

multipath.conf(5) man page on your system
Configuration file defaults

5.6. Configuration file overrides section

The overrides section recognizes the optional protocol subsection, and can contain multiple protocol subsections. The system matches path devices against the protocol subsection, using the mandatory type attribute. Attributes in a matching protocol subsection have priority over attributes in the rest of the overrides section. If there are multiple matching protocol subsections, later entries have higher priority.

The protocol subsection recognizes the following mandatory attribute:

Table 5.4. Protocol subsection attribute
Attribute	Description
`type`	Specifies the protocol string of the path device. Possible values include:
	`scsi:fcp`, `scsi:spi`, `scsi:ssa`, `scsi:sbp`, `scsi:srp`, `scsi:iscsi`, `scsi:sas`, `scsi:adt`, `scsi:ata`, `scsi:unspec`, `ccw`, `cciss`, `nvme`, `undef`
	This attribute is not a regular expression. The path device protocol string must match exactly.

The attributes in the following list are optional for the protocol subsection. If you do not set them, default values from the overrides, devices or defaults sections apply.

fast_io_fail_tmo
dev_loss_tmo
eh_deadline

Additional resources

multipath.conf(5) man page on your system
Configuration file defaults

5.7. DM Multipath overrides of the device timeout

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

The replacement_timeout configuration option globally overrides the recovery_tmo value for all iSCSI devices.
For all iSCSI devices that are managed by DM Multipath, the fast_io_fail_tmo option in DM Multipath globally overrides the recovery_tmo value.
The fast_io_fail_tmo option in DM Multipath also overrides the fast_io_fail_tmo option in Fibre Channel devices.

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.

5.8. Modifying multipath settings for specific devices

In the multipaths section of the multipath.conf configuration file, you can add configurations that are specific to an individual multipath device, referenced by the mandatory WWID parameter.

These defaults are used by DM Multipath and override attributes set in the overrides, defaults, and devices sections of the multipath.conf file. There can be any number of multipath subsections in the multipaths section.

Procedure

Modify the multipaths section for specific multipath device. 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 attribute 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
        }
}

Validate the /etc/multipath.conf file after modifying the multipath configuration file by running one of the following commands:
- To display any configuration errors, run:
```
# multipath -t > /dev/null
```
- To display the new configuration with the changes added, run:
```
# multipath -t
```
Reload the /etc/multipath.conf file and reconfigure the multipathd daemon for changes to take effect:
```
# service multipathd reload
```

Additional resources

multipath.conf(5) man page on your system

5.9. Modifying the multipath configuration for specific devices with protocol

You can configure multipath device paths, based on their transport protocol. By using the protocol subsection of the overrides section in the /etc/multipath.conf file, you can override the multipath configuration settings on certain paths. This enables access to multipath devices over multiple transport protocols, like Fiber Channel (FC) or Internet Small Computer Systems Interface (iSCSI).

Options set in the protocol subsection override values in the overrides, devices and defaults sections. These options apply only to devices using a transport protocol which matches the type parameter of the subsection.

Prerequisites

You have configured Device Mapper (DM) multipath in your system.
You have multipath devices where not all paths use the same transport protocol.

Procedure

View the specific path protocol by running the following:

# multipathd show paths format "%d %P"
dev protocol
sda scsi:ata
sdb scsi:fcp
sdc scsi:fcp

Edit the overrides section of the /etc/multipath.conf file, by adding protocol subsections for each multipath type.

The overrides section can include multiple protocol subsections.

Important

The protocol subsection must include a type parameter. The configuration of all paths with a matching type parameter is then updated with the rest of the parameters listed in the protocol subsection.

Settings for path devices, which use the scsi:fcp protocol:

overrides {
        dev_loss_tmo 60
        fast_io_fail_tmo 8
        protocol {
                type "scsi:fcp"
                dev_loss_tmo 70
                fast_io_fail_tmo 10
                eh_deadline 360
        }
}

Settings for path devices, which use the scsi:iscsi protocol:

overrides {
        dev_loss_tmo 60
        fast_io_fail_tmo 8
        protocol {
                type "scsi:iscsi"
                dev_loss_tmo 60
                fast_io_fail_tmo 120
        }
}

Settings for path devices, which use all other protocols:

overrides {
        dev_loss_tmo 60
        fast_io_fail_tmo 8
        protocol {
                type "<type of protocol>"
                dev_loss_tmo 60
                fast_io_fail_tmo 8
        }
}

Additional resources

multipath.conf(5) man page

5.10. Modifying multipath settings for storage controllers

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.

Procedure

View the information about the default configuration value, including supported devices:
```
# multipathd show config
# multipath -t
```
Many devices that support multipathing are included by default in a multipath configuration.
Optional: If you need to modify the default configuration values, 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.
Add a device that is not configured automatically by default to the devices section of the configuration file by setting the vendor and product parameters. Find these values by opening the /sys/block/device_name/device/vendor and /sys/block/device_name/device/model files where device_name is the device to be multipathed, as mentioned in the following example:
```
# cat /sys/block/sda/device/vendor
WINSYS
# cat /sys/block/sda/device/model
SF2372
```
Optional: Specify the additional parameters depending on your specific device:
active/active device
Usually there is no need to set additional parameters in this case. If required, you might set path_grouping_policy to multibus. Other parameters you may need to set are no_path_retry and rr_min_io.
active/passive device
If 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 means that you have set the path_checker to tur, which 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 might 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
#	}
#}
```
Validate the /etc/multipath.conf file after modifying the multipath configuration file by running one of the following commands:
- To display any configuration errors, run:
```
# multipath -t > /dev/null
```
- To display the new configuration with the changes added, run:
```
# multipath -t
```
Reload the /etc/multipath.conf file and reconfigure the multipathd daemon for changes to take effect:
```
# service multipathd reload
```

Additional resources

multipath.conf(5) and multipathd(8) man pages on your system

5.11. Setting multipath values for all devices

Using the overrides section of the multipath.conf configuration file, you can set a configuration value for all of your devices. This section supports all 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.

DM Multipath uses these attributes 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.

Procedure

Override device specific settings. For example, you might want all devices to set no_path_retry to fail. Use the following command to turn off queueing, when all paths have failed. This overrides any device specific settings.
```
overrides {
        no_path_retry fail
}
```
Validate the /etc/multipath.conf file after modifying the multipath configuration file by running one of the following commands:
- To display any configuration errors, run:
```
# multipath -t > /dev/null
```
- To display the new configuration with the changes added, run:
```
# multipath -t
```
Reload the /etc/multipath.conf file and reconfigure the multipathd daemon for changes to take effect:
```
# service multipathd reload
```

Additional resources

multipath.conf(5) man page on your system

Chapter 5. Modifying the DM Multipath configuration file

5.1. Configuration file overview

5.2. Configuration file defaults

5.3. Modifying multipath configuration file defaults

5.4. Configuration file multipaths section

5.5. Configuration file devices section

5.6. Configuration file overrides section

5.7. DM Multipath overrides of the device timeout

5.8. Modifying multipath settings for specific devices

5.9. Modifying the multipath configuration for specific devices with protocol

5.10. Modifying multipath settings for storage controllers

5.11. Setting multipath values for all devices

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