DOKK / manpages / debian 10 / multipath-tools / multipath.conf.5.en
MULTIPATH.CONF(5) File Formats Manual MULTIPATH.CONF(5)

multipath.conf - multipath daemon configuration file.

/etc/multipath.conf is the configuration file for the multipath daemon. It is used to overwrite the built-in configuration table of multipathd. Any line whose first non-white-space character is a '#' is considered a comment line. Empty lines are ignored.

Currently used multipathd configuration can be displayed with the multipath -t or multipathd show config command.

The configuration file contains entries of the form:


<section> {
<attribute> <value>
...
<subsection> {
<attribute> <value>
...
}
}

Each section contains one or more attributes or subsections. The recognized keywords for attributes or subsections depend on the section in which they occur.

<attribute> and <value> must be on a single line. <attribute> is one of the keywords listed in this man page. <value> is either a simple word (containing no whitespace and none of the characters '"', '#', and '!') or one string enclosed in double quotes ("..."). Outside a quoted string, text starting with '#', and '!' is regarded as a comment and ignored until the end of the line. Inside a quoted string, '#' and '!' are normal characters, and whitespace is preserved. To represent a double quote character inside a double quoted string, use two consecutive double quotes ('""'). Thus '2.5" SSD' can be written as "2.5"" SSD".

Opening braces ('{') must follow the (sub)section name on the same line. Closing braces ('}') that mark the end of a (sub)section must be the only non-whitespace character on the line. Whitespace is ignored except inside double quotes, thus the indentation shown in the above example is helpful for human readers but not mandatory.

Note on regular expressions: The multipath.conf syntax allows many attribute values to be specified as POSIX Extended Regular Expressions (see regex(7)). These regular expressions are case sensitive and not anchored, thus the expression "bar" matches "barbie", "rhabarber", and "wunderbar", but not "Barbie". To avoid unwanted substring matches, standard regular expression syntax using the special characters "^" and "$" can be used.

The following section keywords are recognized:

This section defines default values for attributes which are used whenever no values are given in the appropriate device or multipath sections.
This section defines which devices should be excluded from the multipath topology discovery.
This section defines which devices should be included in the multipath topology discovery, despite being listed in the blacklist section.
This section defines the multipath topologies. They are indexed by a World Wide Identifier(WWID). For details on the WWID generation see section WWID generation below. Attributes set in this section take precedence over all others.
This section defines the device-specific settings. Devices are identified by vendor, product, and revision.
This section defines values for attributes that should override the device-specific settings for all devices.

The defaults section recognizes the following keywords:

Default verbosity. Higher values increase the verbosity level. Valid levels are between 0 and 6.
Interval between two path checks in seconds. For properly functioning paths, the interval between checks will gradually increase to max_polling_interval. This value will be overridden by the WatchdogSec setting in the multipathd.service definition if systemd is used.
Maximal interval between two path checks in seconds.
Enable reassigning of device-mapper maps. With this option multipathd will remap existing device-mapper maps to always point to multipath device, not the underlying block devices. Possible values are yes and no.
Directory where the dynamic shared objects are stored. Defined at compile time, commonly /lib64/multipath/ or /lib/multipath/.
The default path selector algorithm to use; they are offered by the kernel multipath target. There are three selector algorithms:
Loop through every path in the path group, sending the same amount of I/O to each. Some aspects of behavior can be controlled with the attributes: rr_min_io, rr_min_io_rq and rr_weight.
(Since 2.6.31 kernel) Choose the path for the next bunch of I/O based on the amount of outstanding I/O to the path.
(Since 2.6.31 kernel) Choose the path for the next bunch of I/O based on the amount of outstanding I/O to the path and its relative throughput.
The default path grouping policy to apply to unspecified multipaths. Possible values are:
One path per priority group.
All paths in one priority group.
One priority group per serial number.
One priority group per priority value. Priorities are determined by callout programs specified as a global, per-controller or per-multipath option in the configuration file.
One priority group per target node name. Target node names are fetched in /sys/class/fc_transport/target*/node_name.
The udev attribute providing a unique path identifier for corresponding type of path devices. If this field is configured and matched with type of device, it would override any other methods providing for device unique identifier in config file, and it would activate merging uevents according to the identifier to promote effiecncy in processing uevents. It has no default value, if you want to identify path by udev attribute and to activate merging uevents for SCSI and DASD devices, you can set its value as: uid_attrs "sd:ID_SERIAL dasd:ID_UID".
The udev attribute providing a unique path identifier.
(Superseded by uid_attribute) The default program and args to callout to obtain a unique path identifier. Should be specified with an absolute path.
The name of the path priority routine. The specified routine should return a numeric value specifying the relative priority of this path. Higher number have a higher priority. "none" is a valid value. Currently the following path priority routines are implemented:
Return a constant priority of 1.
Use the sysfs attributes access_state and preferred_path to generate the path priority. This prioritizer accepts the optional prio_arg exclusive_pref_bit.
(Hardware-dependent) Generate the path priority for DGC class arrays as CLARiiON CX/AX and EMC VNX and Unity families.
(Hardware-dependent) Generate the path priority based on the SCSI-3 ALUA settings. This prioritizer accepts the optional prio_arg exclusive_pref_bit.
(Hardware-dependent) Generate the path priority for NetApp ONTAP class and OEM arrays as IBM NSeries.
(Hardware-dependent) Generate the path priority for LSI/Engenio/NetApp RDAC class as NetApp SANtricity E/EF Series, and OEM arrays from IBM DELL SGI STK and SUN.
(Hardware-dependent) Generate the path priority for HP/COMPAQ/DEC HSG80 and MSA/HSV arrays with Active/Standby mode exclusively.
(Hardware-dependent) Generate the path priority for Hitachi AMS families of arrays other than AMS 2000.
Generate a random priority between 1 and 10.
Generate the path priority based on the regular expression and the priority provided as argument. Requires prio_args keyword.
Generate the path priority based on a latency algorithm. Requires prio_args keyword.
(Hardware-dependent) Generate the path priority for some DataCore storage arrays. Requires prio_args keyword.
(iSCSI only) Generate path priority for iSCSI targets based on IP address. Requires prio_args keyword.

The default depends on the detect_prio setting: If detect_prio is yes (default), the default priority algorithm is sysfs (except for NetAPP E-Series, where it is alua). If detect_prio is no, the default priority algorithm is const.

Arguments to pass to to the prio function. This only applies to certain prioritizers:
Needs a value of the form "<hbtl|devname|serial|wwn> <regex1> <prio1> <regex2> <prio2> ..."
Regex can be of SCSI H:B:T:L format. For example: 1:0:.:. , *:0:0:.
Regex can be of device name format. For example: sda , sd.e
Regex can be of serial number format. For example: .*J1FR.*324 . The serial can be looked up through sysfs or by running multipathd show paths format "%z". For example: 0395J1FR904324
Regex can be of the form "host_wwnn:host_wwpn:target_wwnn:target_wwpn" these values can be looked up through sysfs or by running multipathd show paths format "%N:%R:%n:%r". For example: 0x200100e08ba0aea0:0x210100e08ba0aea0:.*:.* , .*:.*:iqn.2009-10.com.redhat.msp.lab.ask-06:.*
Needs a value of the form "io_num=<20> base_num=<10>"
The number of read IOs sent to the current path continuously, used to calculate the average path latency. Valid Values: Integer, [2, 200].
The base number value of logarithmic scale, used to partition different priority ranks. Valid Values: Integer, [2, 10]. And Max average latency value is 100s, min average latency value is 1us. For example: If base_num=10, the paths will be grouped in priority groups with path latency <=1us, (1us, 10us], (10us, 100us], (100us, 1ms], (1ms, 10ms], (10ms, 100ms], (100ms, 1s], (1s, 10s], (10s, 100s], >100s.
If exclusive_pref_bit is set, paths with the preferred path bit set will always be in their own path group.
If exclusive_pref_bit is set, paths with the preferred path bit set will always be in their own path group.
(Mandatory) The preferred "SDS name".
(Optional) The timeout for the INQUIRY, in ms.
(Mandatory) Th preferred IP address, in dotted decimal notation, for iSCSI targets.
Specify any device-mapper features to be used. Syntax is num list where num is the number, between 0 and 8, of features in list. Possible values for the feature list are:
(Deprecated, superseded by no_path_retry) Queue I/O if no path is active. Identical to the no_path_retry with queue value. If both this feature and no_path_retry are set, the latter value takes precedence. See KNOWN ISSUES.
(Since kernel 2.6.24) Number of times to retry pg_init, it must be between 1 and 50.
(Since kernel 2.6.38) Number of msecs before pg_init retry, it must be between 0 and 60000.
(Since kernel 4.8) Select the the queueing mode per multipath device. <mode> can be bio, rq or mq, which corresponds to bio-based, request-based, and block-multiqueue (blk-mq) request-based, respectively. The default depends on the kernel parameter dm_mod.use_blk_mq. It is mq if the latter is set, and rq otherwise.
The default method used to determine the paths state. Possible values are:
(Deprecated) Read the first sector of the device. This checker is being deprecated, please use tur instead.
Issue a TEST UNIT READY command to the device.
(Hardware-dependent) Query the DGC/EMC specific EVPD page 0xC0 to determine the path state for CLARiiON CX/AX and EMC VNX and Unity arrays families.
(Hardware-dependent) Check the path state for HP/COMPAQ/DEC HSG80 and MSA/HSV arrays with Active/Standby mode exclusively.
(Hardware-dependent) Check the path state for LSI/Engenio/NetApp RDAC class as NetApp SANtricity E/EF Series, and OEM arrays from IBM DELL SGI STK and SUN.
(Deprecated) Read the first sector with direct I/O. This checker is being deprecated, it could cause spurious path failures under high load. Please use tur instead.
(Hardware-dependent) Check the path state for HP/COMPAQ Smart Array(CCISS) controllers.
Do not check the device, fallback to use the values retrieved from sysfs
The user_friendly_names prefix.
Tell multipathd how to manage path group failback. To select immediate or a value, it's mandatory that the device has support for a working prioritizer.
Immediately failback to the highest priority pathgroup that contains active paths.
Do not perform automatic failback.
Used to deal with multiple computers accessing the same Active/Passive storage devices. Only perform automatic failback when the first path of a pathgroup becomes active. This keeps a cluster node from automatically failing back when another node requested the failover.
Deferred failback (time to defer in seconds).
Number of I/O requests to route to a path before switching to the next in the same path group. This is only for Block I/O(BIO) based multipath and only apply to round-robin path_selector.
Number of I/O requests to route to a path before switching to the next in the same path group. This is only for Request based multipath and only apply to round-robin path_selector.
Specify the maximum number of file descriptors that can be opened by multipath and multipathd. This is equivalent to ulimit -n. A value of max will set this to the system limit from /proc/sys/fs/nr_open. If this is not set, the maximum number of open fds is taken from the calling process. It is usually 1024. To be safe, this should be set to the maximum number of paths plus 32, if that number is greated than 1024.
If set to priorities the multipath configurator will assign path weights as "path prio * rr_min_io". Possible values are priorities or uniform . Only apply to round-robin path_selector.
Specify what to do when all paths are down. Possible values are:
Number of retries until disable I/O queueing.
For immediate failure (no I/O queueing).
For never stop I/O queueing, similar to queue_if_no_path. See KNOWN ISSUES.
If set to no , when multipathd stops, queueing will be turned off for all devices. This is useful for devices that set no_path_retry. If a machine is shut down while all paths to a device are down, it is possible to hang waiting for I/O to return from the device after multipathd has been stopped. Without multipathd running, access to the paths cannot be restored, and the kernel cannot be told to stop queueing I/O. Setting queue_without_daemon to no , avoids this problem.
Specify the timeout to use for path checkers and prioritizers that issue SCSI commands with an explicit timeout, in seconds.
If set to yes , multipathd will disable queueing when the last path to a device has been deleted.
If set to yes , using the bindings file /etc/multipath/bindings to assign a persistent and unique alias to the multipath, in the form of mpath<n>. If set to no use the WWID as the alias. In either case this be will be overridden by any specific aliases in the multipaths section.
Specify the number of seconds the SCSI layer will wait after a problem has been detected on a FC remote port before failing I/O to devices on that remote port. This should be smaller than dev_loss_tmo. Setting this to off will disable the timeout.
Specify the number of seconds the SCSI layer will wait after a problem has been detected on a FC remote port before removing it from the system. This can be set to "infinity" which sets it to the max value of 2147483647 seconds, or 68 years. It will be automatically adjusted to the overall retry interval no_path_retry * polling_interval if a number of retries is given with no_path_retry and the overall retry interval is longer than the specified dev_loss_tmo value. The Linux kernel will cap this value to 600 if fast_io_fail_tmo is not set. See KNOWN ISSUES.
The full pathname of the binding file to be used when the user_friendly_names option is set.
The full pathname of the WWIDs file, which is used by multipath to keep track of the WWIDs for LUNs it has created multipath devices on in the past.
The full pathname of the prkeys file, which is used by multipathd to keep track of the persistent reservation key used for a specific WWID, when reservation_key is set to file.
If set to once , multipathd logs the first path checker error at logging level 2. Any later errors are logged at level 3 until the device is restored. If set to always , multipathd always logs the path checker error at logging level 2.
This is the service action reservation key used by mpathpersist. 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 the --param-aptpl option is used when registering the key with mpathpersist, :aptpl must be appended to the end of the reservation key.

Alternatively, this can be set to file, which will store the RESERVATION KEY registered by mpathpersist in the prkeys_file. multipathd will then use this key to register additional paths as they appear. When the registration is removed, the RESERVATION KEY is removed from the prkeys_file. The prkeys file will automatically keep track of whether the key was registered with --param-aptpl.

Set the 'all targets ports' flag when registering keys with mpathpersist. Some arrays automatically set and clear registration keys on all target ports from a host, instead of per target port per host. The ALL_TG_PT flag must be set to successfully use mpathpersist on these arrays. Setting this option is identical to calling mpathpersist with --param-alltgpt
(Obsolete for kernels >= 4.3) If set to yes and the SCSI layer has already attached a hardware_handler to the device, multipath will not force the device to use the hardware_handler specified by mutipath.conf. If the SCSI layer has not attached a hardware handler, multipath will continue to use its configured hardware handler.

The default is: yes

Important Note: Linux kernel 4.3 or newer always behaves as if "retain_attached_hw_handler yes" was set.

If set to yes , multipath will try to detect if the device supports SCSI-3 ALUA. If so, the device will automatically use the sysfs prioritizer if the required sysf attributes access_state and preferred_path are supported, or the alua prioritizer if not. If set to no , the prioritizer will be selected as usual.
if set to yes , multipath will try to detect if the device supports SCSI-3 ALUA. If so, the device will automatically use the tur checker. If set to no , the checker will be selected as usual.
If set to yes , multipathd will call the path checkers in sync mode only. This means that only one checker will run at a time. This is useful in the case where many multipathd checkers running in parallel causes significant CPU pressure.
If set to yes , multipathd will start a new path checker loop after exactly one second, so that each path check will occur at exactly polling_interval seconds. On busy systems path checks might take longer than one second; here the missing ticks will be accounted for on the next round. A warning will be printed if path checks take longer than polling_interval seconds.
If set to yes , multipathd will do a deferred remove instead of a regular remove when the last path device has been deleted. This means that if the multipath device is still in use, it will be freed when the last user closes it. If path is added to the multipath device before the last user closes it, the deferred remove will be canceled.
This parameter controls how multipath chooses the names of partition devices of multipath maps if a multipath map is renamed (e.g. if a map alias is added or changed). If this parameter is set to a string other than "/UNSET/" (even the empty string), multipath inserts that string between device name and partition number to construct the partition device name. Otherwise (i.e. if this parameter is unset or has the value "/UNSET/"), the behavior depends on the map name: if it ends in a digit, a "p" is inserted between name and partition number; otherwise, the partition number is simply appended. Distributions may use a non-null default value for this option; in this case, the user must set it to "/UNSET/" to obtain the original <unset> behavior. Use multipath -T to check the current settings.
If set to anything other than "", multipath will search this directory alphabetically for file ending in ".conf" and it will read configuration information from them, just as if it was in /etc/multipath.conf. config_dir must either be "" or a fully qualified directory name.
One of the four parameters of supporting path check based on accounting IO error such as intermittent error. When a path failed event occurs twice in marginal_path_double_failed_time seconds due to an IO error and all the other three parameters are set, multipathd will fail the path and enqueue this path into a queue of which members are sent a couple of continuous direct reading asynchronous IOs at a fixed sample rate of 10HZ to start IO error accounting process.
One of the four parameters of supporting path check based on accounting IO error such as intermittent error. If it is set to a value no less than 120, when a path fail event occurs twice in marginal_path_double_failed_time second due to an IO error, multipathd will fail the path and enqueue this path into a queue of which members are sent a couple of continuous direct reading asynchronous IOs at a fixed sample rate of 10HZ to start the IO accounting process for the path will last for marginal_path_err_sample_time. If the rate of IO error on a particular path is greater than the marginal_path_err_rate_threshold, then the path will not reinstate for marginal_path_err_recheck_gap_time seconds unless there is only one active path. After marginal_path_err_recheck_gap_time expires, the path will be requeueed for rechecking. If checking result is good enough, the path will be reinstated.
The error rate threshold as a permillage (1/1000). One of the four parameters of supporting path check based on accounting IO error such as intermittent error. Refer to marginal_path_err_sample_time. If the rate of IO errors on a particular path is greater than this parameter, then the path will not reinstate for marginal_path_err_recheck_gap_time seconds unless there is only one active path.
One of the four parameters of supporting path check based on accounting IO error such as intermittent error. Refer to marginal_path_err_sample_time. If this parameter is set to a positive value, the failed path of which the IO error rate is larger than marginal_path_err_rate_threshold will be kept in failed state for marginal_path_err_recheck_gap_time seconds. When marginal_path_err_recheck_gap_time seconds expires, the path will be requeueed for checking. If checking result is good enough, the path will be reinstated, or else it will keep failed.
If set to a value greater than 0, multipathd will watch paths that have recently become valid for this many checks. If they fail again while they are being watched, when they next become valid, they will not be used until they have stayed up for delay_wait_checks checks.
If set to a value greater than 0, when a device that has recently come back online fails again within delay_watch_checks checks, the next time it comes back online, it will marked and delayed, and not used until it has passed delay_wait_checks checks.
This option controls whether multipath and multipathd try to create multipath maps over non-blacklisted devices they encounter. This matters a) when a device is encountered by multipath -u during udev rule processing (a device is blocked from further processing by higher layers - such as LVM - if and only if it´s considered a valid multipath device path), and b) when multipathd detects a new device. The following values are possible:
Both multipath and multipathd treat only such devices as multipath devices which have been part of a multipath map previously, and which are therefore listed in the wwids_file. Users can manually set up multipath maps using the multipathd add map command. Once set up manually, the map is remembered in the wwids file and will be set up automatically in the future.
Multipath behaves like strict. Multipathd behaves like greedy.
Both multipathd and multipath treat a device as multipath device if the conditions for strict are met, or if at least two non-blacklisted paths with the same WWID have been detected.
Both multipathd and multipath treat every non-blacklisted device as multipath device path.
This differs from find_multipaths yes only in the way it treats new devices for which only one path has been detected yet. When such a device is first encounted in udev rules, it is treated as a multipath device. multipathd waits whether additional paths with the same WWID appears. If that happens, it sets up a multipath map. If it doesn´t happen until a timeout expires, or if setting up the map fails, a new uevent is triggered for the device; at second encounter in the udev rules, the device will be treated as non-multipath and passed on to upper layers. Note: this may cause delays during device detection if there are single-path devices which aren´t blacklisted.
Timeout, in seconds, to wait for additional paths after detecting the first one, if find_multipaths "smart" (see above) is set. If the value is positive, this timeout is used for all unknown, non-blacklisted devices encountered. If the value is negative (recommended), it's only applied to "known" devices that have an entry in multipath's hardware table, either in the built-in table or in a device section; other ("unknown") devices will use a timeout of only 1 second to avoid booting delays. The value 0 means "use the built-in default". If find_multipath has a value other than smart, this option has no effect.
CLI receive timeout in milliseconds. For larger systems CLI commands might timeout before the multipathd lock is released and the CLI command can be processed. This will result in errors like "timeout receiving packet" to be returned from CLI commands. In these cases it is recommended to increase the CLI timeout to avoid those issues.
Sets the number of times multipathd will try to retrigger a uevent to get the WWID.
Sets the amount of time, in seconds, to wait between retriggers.
Controls how many seconds multipathd will wait, after a new multipath device is created, to receive a change event from udev for the device, before automatically enabling device reloads. Usually multipathd will delay reloads on a device until it receives a change uevent from the initial table load.
If set to yes , kpartx will not automatically create partitions on the device.
If set to yes, multipathd will check the path wwid on change events, and if it has changed from the wwid of the multipath device, multipathd will disable access to the path until the wwid changes back.
This sets how may times multipath will retry removing a device that is in-use. Between each attempt, multipath will sleep 1 second.
Sets the max_sectors_kb device parameter on all path devices and the multipath device to the specified value.
Sets the number of seconds that multipath will wait 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 on makes multipath immediately mark a device with only ghost paths as ready.

The blacklist section is used to exclude specific devices from the multipath topology. It is most commonly used to exclude local disks or non-disk devices (such as LUNs for the storage array controller) from being handled by multipath-tools.

The blacklist_exceptions section is used to revert the actions of the blacklist section. This allows one to selectively include ("whitelist") devices which would normally be excluded via the blacklist section. A common usage is to blacklist "everything" using a catch-all regular expression, and create specific blacklist_exceptions entries for those devices that should be handled by multipath-tools.

The following keywords are recognized in both sections. The defaults are empty unless explicitly stated.

Regular expression matching the device nodes to be excluded/included.

The default blacklist consists of the regular expressions "^(ram|raw|loop|fd|md|dm-|sr|scd|st|dcssblk)[0-9]" and "^(td|hd|vd)[a-z]". This causes virtual devices, non-disk devices, and some other device types to be excluded from multipath handling by default.

Regular expression for the World Wide Identifier of a device to be excluded/included.
Subsection for the device description. This subsection recognizes the vendor and product keywords. Both are regular expressions. For a full description of these keywords please see the devices section description.
Regular expression for an udev property. All devices that have matching udev properties will be excluded/included. The handling of the property keyword is special, because devices must have at least one whitelisted udev property; otherwise they're treated as blacklisted, and the message "blacklisted, udev property missing" is displayed in the logs.

The default blacklist exception is: (SCSI_IDENT_|ID_WWN), causing well-behaved SCSI devices and devices that provide a WWN (World Wide Number) to be included, and all others to be excluded.

Regular expression for the protocol of a device to be excluded/included.

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 multipathd show paths format "%d %P"

For every device, these 5 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's excluded from handling by multipathd, and the later criteria aren't evaluated any more. For each criterion, the whitelist takes precedence over the blacklist if a device matches both.

Note: Besides the blacklist and whitelist, other configuration options such as find_multipaths have an impact on whether or not a given device is handled by multipath-tools.

The multipaths section allows setting attributes of multipath maps. The attributes that are set via the multipaths section (see list below) take precedence over all other configuration settings, including those from the overrides section.

The only recognized attribute for the multipaths section is the multipath subsection. If there are multiple multipath subsections matching a given WWID, the contents of these sections are merged, and settings from later entries take precedence.

The multipath subsection recognizes the following attributes:

(Mandatory) World Wide Identifier. Detected multipath maps are matched agains this attribute. Note that, unlike the wwid attribute in the blacklist section, this is not a regular expression or a substring; WWIDs must match exactly inside the multipaths section.
Symbolic name for the multipath map. This takes precedence over a an entry for the same WWID in the bindings_file.

The following attributes are optional; if not set the default values are taken from the overrides, devices, or defaults section:

multipath-tools have a built-in device table with reasonable defaults for more than 100 known multipath-capable storage devices. The devices section can be used to override these settings. If there are multiple matches for a given device, the attributes of all matching entries are applied to it. If an attribute is specified in several matching device subsections, later entries take precedence. Thus, entries in files under config_dir (in reverse alphabetical order) have the highest precedence, followed by entries in multipath.conf; the built-in hardware table has the lowest precedence. Inside a configuration file, later entries have higher precedence than earlier ones.

The only recognized attribute for the devices section is the device subsection. Devices detected in the system are matched against the device entries using the vendor, product, and revision fields, which are all POSIX Extended regular expressions (see regex(7)).

The vendor, product, and revision fields that multipath or multipathd detect for devices in a system depend on the device type. For SCSI devices, they correspond to the respective fields of the SCSI INQUIRY page. In general, the command 'multipathd show paths format "%d %s"' command can be used to see the detected properties for all devices in the system.

The device subsection recognizes the following attributes:

(Mandatory) Regular expression to match the vendor name.
(Mandatory) Regular expression to match the product name.
Regular expression to match the product revision. If not specified, any revision matches.
Products with the given vendor matching this string are blacklisted. This is equivalent to a device entry in the blacklist section with the vendor attribute set to this entry's vendor, and the product attribute set to the value of product_blacklist.
The user_friendly_names prefix to use for this device type, instead of the default "mpath".
The hardware handler to use for this device type. The following hardware handler are implemented:
1 emc
(Hardware-dependent) Hardware handler for DGC class arrays as CLARiiON CX/AX and EMC VNX and Unity families.
1 rdac
(Hardware-dependent) Hardware handler for LSI/Engenio/NetApp RDAC class as NetApp SANtricity E/EF Series, and OEM arrays from IBM DELL SGI STK and SUN.
1 hp_sw
(Hardware-dependent) Hardware handler for HP/COMPAQ/DEC HSG80 and MSA/HSV arrays with Active/Standby mode exclusively.
1 alua
(Hardware-dependent) Hardware handler for SCSI-3 ALUA compatible arrays.

The default is: <unset>

Important Note: Linux kernels 4.3 and newer automatically attach a device handler to known devices (which includes all devices supporting SCSI-3 ALUA) and disallow changing the handler afterwards. Setting hardware_handler for such devices on these kernels has no effect.

The following attributes are optional; if not set the default values are taken from the defaults section:

The overrides section recognizes the following optional attributes; if not set the values are taken from the devices or defaults sections:

Multipath uses a World Wide Identification (WWID) to determine which paths belong to the same device. Each path presenting the same WWID is assumed to point to the same device.

The WWID is generated by four methods (in the order of preference):

The WWID is derived from udev attributes by matching the device node name. See description of uid_attrs in the defaults section above.
Use the specified external program; cf getuid_callout above. Care should be taken when using this method; the external program needs to be loaded from disk for execution, which might lead to deadlock situations in an all-paths-down scenario.
Use the value of the specified udev attribute; cf uid_attribute above. This method is preferred to getuid_callout as multipath does not need to call any external programs here. However, under certain circumstances udev might not be able to generate the requested variable.
If none of the getuid_callout or uid_attribute parameters are present multipath will try to use the sysfs attribute vpd_pg83 to generate the WWID.

The usage of queue_if_no_path option can lead to D state processes being hung and not killable in situations where all the paths to the LUN go offline. It is advisable to use the no_path_retry option instead.

The use of queue_if_no_path or no_path_retry might lead to a deadlock if the dev_loss_tmo setting results in a device being removed while I/O is still queued. The multipath daemon will update the dev_loss_tmo setting accordingly to avoid this deadlock. Hence if both values are specified the order of precedence is no_path_retry, queue_if_no_path, dev_loss_tmo.

udev(8), dmsetup(8), multipath(8), multipathd(8).

multipath-tools was developed by Christophe Varoqui, <christophe.varoqui@opensvc.com> and others.

2018-05-21 Linux