NAME¶

DESCRIPTION¶

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

SYNTAX¶

<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:

defaults

This section defines default values for attributes which are used whenever no values are given in the appropriate device or multipath sections.

blacklist

This section defines which devices should be excluded from the multipath topology discovery.

blacklist_exceptions

This section defines which devices should be included in the multipath topology discovery, despite being listed in the blacklist section.

multipaths

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.

devices

This section defines the device-specific settings. Devices are identified by vendor, product, and revision.

overrides

This section defines values for attributes that should override the device-specific settings for all devices.

defaults section¶

verbosity

Default verbosity. Higher values increase the verbosity level. Valid levels are between 0 and 6.

polling_interval

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.

max_polling_interval

Maximal interval between two path checks in seconds.

reassign_maps

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.

multipath_dir

Directory where the dynamic shared objects are stored. Defined at compile time, commonly /lib64/multipath/ or /lib/multipath/.

path_selector

The default path selector algorithm to use; they are offered by the kernel multipath target. There are three selector algorithms:

path_grouping_policy

The default path grouping policy to apply to unspecified multipaths. Possible values are:

uid_attrs

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".

uid_attribute

The udev attribute providing a unique path identifier.

getuid_callout

(Superseded by uid_attribute) The default program and args to callout to obtain a unique path identifier. Should be specified with an absolute path.

prio

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:

prio_args

Arguments to pass to to the prio function. This only applies to certain prioritizers:

features

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:

path_checker

The default method used to determine the paths state. Possible values are:

alias_prefix

The user_friendly_names prefix.

failback

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.

rr_min_io

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.

rr_min_io_rq

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.

max_fds

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.

rr_weight

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.

no_path_retry

Specify what to do when all paths are down. Possible values are:

queue_without_daemon

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.

checker_timeout

Specify the timeout to use for path checkers and prioritizers that issue SCSI commands with an explicit timeout, in seconds.

flush_on_last_del

If set to yes , multipathd will disable queueing when the last path to a device has been deleted.

user_friendly_names

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.

fast_io_fail_tmo

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.

dev_loss_tmo

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.

bindings_file

The full pathname of the binding file to be used when the user_friendly_names option is set.

wwids_file

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.

prkeys_file

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.

log_checker_err

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.

reservation_key

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.

all_tg_pt

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

retain_attached_hw_handler

(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.

detect_prio

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.

detect_checker

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.

force_sync

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.

strict_timing

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.

deferred_remove

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.

partition_delimiter

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.

config_dir

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.

marginal_path_double_failed_time

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.

marginal_path_err_sample_time

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.

marginal_path_err_rate_threshold

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.

marginal_path_err_recheck_gap_time

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.

delay_watch_checks

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.

delay_wait_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.

find_multipaths

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:

find_multipaths_timeout

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.

uxsock_timeout

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.

retrigger_tries

Sets the number of times multipathd will try to retrigger a uevent to get the WWID.

retrigger_delay

Sets the amount of time, in seconds, to wait between retriggers.

missing_uev_wait_timeout

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.

skip_kpartx

If set to yes , kpartx will not automatically create partitions on the device.

disable_changed_wwids

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.

remove_retries

This sets how may times multipath will retry removing a device that is in-use. Between each attempt, multipath will sleep 1 second.

max_sectors_kb

Sets the max_sectors_kb device parameter on all path devices and the multipath device to the specified value.

ghost_delay

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.

blacklist and blacklist_exceptions sections¶

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.

devnode

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

wwid

Regular expression for the World Wide Identifier of a device to be excluded/included.

device

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.

property

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.

protocol

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

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.

multipaths 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:

wwid

(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.

alias

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:

devices section¶

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:

vendor

(Mandatory) Regular expression to match the vendor name.

product

(Mandatory) Regular expression to match the product name.

revision

Regular expression to match the product revision. If not specified, any revision matches.

product_blacklist

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.

alias_prefix

The user_friendly_names prefix to use for this device type, instead of the default "mpath".

hardware_handler

The hardware handler to use for this device type. The following hardware handler are implemented:

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

overrides section¶

WWID generation¶

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

uid_attrs

The WWID is derived from udev attributes by matching the device node name. See description of uid_attrs in the defaults section above.

getuid_callout

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.

uid_attribute

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.

vpd_pg83

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.

KNOWN ISSUES¶

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.

SEE ALSO¶

AUTHORS¶