Chapter 4. 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. For information on the default configuration values, including supported devices, run either of the following commands.
#multipathd show config
#multipath -t
You can override the default configuration values for DM Multipath by editing the /etc/multipath.conf
configuration file. If necessary, you can also add a storage array that is not supported by default to the configuration file.
You can run set up multipathing in the initramfs
file system. 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.
In the multipath configuration file, you need to specify only the sections that you need for your configuration, or that you wish 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.
The configuration file allows regular expression description syntax.
Further information about the configuration file can be found on the multipath.conf
(5) man page.
4.1. 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 candidates that would otherwise be blacklisted 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
, anddefaults
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 adevices
subsection for your array. - overrides
-
Settings that are applied to all devices. These values overwrite what is specified in the
devices
anddefaults
sections of the configuration file.
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.
4.2. 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 recovery_tmo
values:
-
The
replacement_timeout
configuration option globally overrides therecovery_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 therecovery_tmo
value.The
fast_io_fail_tmo
option in DM Multipath also overrides thefast_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.
4.3. Blacklisting devices from DM Multipath
The blacklist
section of the multipath configuration file specifies the devices that will not be used when the system configures multipath devices. Devices that are blacklisted will not be grouped into a multipath device.
If the find_multipaths
configuration parameter is set to off
, multipath always tries to create a multipath device for every path that is not explicitly blacklisted. If the find_multipaths
configuration parameter is set to on
, then multipath will create a device only if one of three conditions are met:
- There are at least two paths that are not blacklisted with the same WWID.
-
The user manually forces the creation of the device by specifying a device with the
multipath
command. A path has the same WWID as a multipath device that was previously created (even if that multipath device does not currently exist). Whenever a multipath device is created, multipath remembers the WWID of the device so that it will automatically create the device again as soon as it sees a path with that WWID. This allows you to have multipath automatically choose the correct paths to make into multipath devices, without have to edit the multipath blacklist.
If you have previously created a multipath device without using the
find_multipaths
parameter and then you later set the parameter toon
, you may need to remove the WWIDs of any device you do not want created as a multipath device from the/etc/multipath/wwids
file. The following shows a sample/etc/multipath/wwids
file. The WWIDs are enclosed by slashes (/):# Multipath wwids, Version : 1.0 # NOTE: This file is automatically maintained by multipath and multipathd. # You should not need to edit this file in normal circumstances. # # Valid WWIDs: /3600d0230000000000e13955cc3757802/ /3600d0230000000000e13955cc3757801/ /3600d0230000000000e13955cc3757800/ /3600d02300069c9ce09d41c31f29d4c00/ /SWINSYS SF2372 0E13955CC3757802/ /3600d0230000000000e13955cc3757803/
In addition to on
and off
, you can also set find_multipaths
to the following values:
-
strict
: multipath never accepts paths that have not previously been multipathed and are therefore not in the/etc/multipath/wwids
file. -
smart
: multipath always accepts non-blacklisted devices in udev as soon as they appear but ifmultipathd
does not create the device within a timeout set with thefind_multipaths_timeout
parameter, it will release its claim on the device. For information on thefind_multipaths_timeout
parameter, see themultipath.conf
(5) man page.
The built-in default value of find_multipaths
is off
. The default multipath.conf
file created by mpathconf
, however, will set the value of find_multipaths
to on
.
For more information on the values you can set for find_multipaths
, see the multipath.conf
(5) man page.
With the find_multipaths
parameter set to on
, you need to blacklist only the devices with multiple paths that you do not want to be multipathed. Because of this, it will generally not be necessary to blacklist devices.
If you do need to blacklist devices, you can blacklist devices by WWID, device name, device type, property, and protocol. For every device, these five blacklist criteria are evaluated in the the order "property, devnode, device, protocol, wwid". If a device turns out to be blacklisted by any criterion, it is excluded from handling by multipathd
, and the later criteria are not evaluated. For each criterion, the whitelist takes precedence over the blacklist if a device matches both.
By default, a variety of device types are blacklisted, even after you comment out the initial blacklist section of the configuration file. For information, see Section 4.3.2, “Blacklisting by device name”.
4.3.1. Blacklisting by WWID
You can specify individual devices to blacklist by their World-Wide IDentification with a wwid
entry in the blacklist
section of the configuration file.
The following example shows the lines in the configuration file that would blacklist a device with a WWID of 26353900f02796769.
blacklist { wwid 26353900f02796769 }
4.3.2. Blacklisting by device name
You can blacklist device types by device name so that they will not be grouped into a multipath device by specifying a devnode
entry in the blacklist
section of the configuration file.
The following example shows the lines in the configuration file that would blacklist all SCSI devices, since it blacklists all sd* devices.
blacklist { devnode "^sd[a-z]" }
You can use a devnode
entry in the blacklist
section of the configuration file to specify individual devices to blacklist rather than all devices of a specific type. This is not recommended, however, since unless it is statically mapped by udev
rules, there is no guarantee that a specific device will have the same name on reboot. For example, a device name could change from /dev/sda
to /dev/sdb
on reboot.
By default, the following devnode
entries are compiled in the default blacklist; the devices that these entries blacklist do not generally support DM Multipath. To enable multipathing on any of these devices, you would need to specify them in the blacklist_exceptions
section of the configuration file, as described in Section 4.3.6, “Blacklist exceptions”.
blacklist { devnode "^(ram|raw|loop|fd|md|dm-|sr|scd|st)[0-9]*" devnode "^(td|ha)d[a-z]" }
4.3.3. Blacklisting by device type
You can specify specific device types in the blacklist
section of the configuration file with a device
section. The following example blacklists all IBM DS4200 and HP devices.
blacklist { device { vendor "IBM" product "3S42" #DS4200 Product 10 } device { vendor "HP" product ".*" } }
4.3.4. Blacklisting by udev property
The blacklist
and blacklist_exceptions
sections of the multipath.conf
configuration file support the property
parameter. This parameter allows users to blacklist certain types of devices. The property
parameter takes a regular expression string that is matched against the udev
environment variable name for the device.
The following example blacklists all devices with the udev property ID_ATA
.
blacklist { property "ID_ATA" }
4.3.5. Blacklisting by device protocol
You can specify the protocol for a device to be excluded from multipathing in the blacklist
section of the configuration file with a protocol
section. The protocol strings that multipath recognizes are scsi:fcp, scsi:spi, scsi:ssa, scsi:sbp, scsi:srp, scsi:iscsi, scsi:sas, scsi:adt, scsi:ata, scsi:unspec, ccw, cciss, nvme, and undef. The protocol that a path is using can be viewed by running the command multipathd show paths format "%d %P"
.
The following example blacklists all devices with an undefined protocol or an unknown SCSI transport type.
blacklist { protocol "scsi:unspec" protocol "undef" }
4.3.6. Blacklist exceptions
You can use the blacklist_exceptions
section of the configuration file to enable multipathing on devices that have been blacklisted by default.
For example, if you have a large number of devices and want to multipath only one of them (with the WWID of 3600d0230000000000e13955cc3757803), instead of individually blacklisting each of the devices except the one you want, you could instead blacklist all of them, and then allow only the one you want by adding the following lines to the /etc/multipath.conf
file.
blacklist { wwid ".*" } blacklist_exceptions { wwid "3600d0230000000000e13955cc3757803" }
When specifying devices in the blacklist_exceptions
section of the configuration file, you must specify the exceptions in the same way they were specified in the blacklist. For example, a WWID exception will not apply to devices specified by a devnode
blacklist entry, even if the blacklisted device is associated with that WWID. Similarly, devnode
exceptions apply only to devnode
entries, and device
exceptions apply only to device entries.
The property
parameter works differently than the other blacklist_exception
parameters. If the parameter is set, the device must have a udev
variable that matches. Otherwise, the device is blacklisted. This parameter allows users to blacklist SCSI devices that multipath should ignore, such as USB sticks and local hard drives. To allow only SCSI devices that could reasonably be multipathed, set this parameter to SCSI_IDENT_|ID_WWN)
as in the following example.
blacklist_exceptions { property "(SCSI_IDENT_|ID_WWN)" }
4.4. Modifying multipath configuration file defaults
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.
4.5. Modifying multipath settings for specific devices
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
}
}
4.6. 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.
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 # } #}
4.7. Setting multipath values for all devices
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.