Provided by: multipath-tools_0.8.8-1ubuntu1.22.04.4_amd64 
NAME
multipath.conf - multipath daemon configuration file.
DESCRIPTION
/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.
SYNTAX
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:
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
The defaults section recognizes the following keywords:
verbosity Default verbosity. Higher values increase the verbosity level. Valid levels are between
0 and 6.
The default is: 2
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.
The default is: 5
max_polling_interval
Maximal interval between two path checks in seconds.
The default is: 4 * polling_interval
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.
The default is: no
multipath_dir This option is deprecated, and will be removed in a future release. Directory where the
dynamic shared objects are stored. Defined at compile time, commonly /lib64/multipath/
or /lib/multipath/.
The default is: <system dependent>
path_selector The default path selector algorithm to use; they are offered by the kernel multipath
target:
round-robin 0
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.
queue-length 0
(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.
service-time 0
(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.
historical-service-time 0
(Since 5.8 kernel) Choose the path for the next bunch of I/O based on the
estimation of future service time based on the history of previous I/O
submitted to each path.
io-affinity 0
(Since 5.11 kernel) Choose the path for the next bunch of I/O based on a CPU
to path mapping the user passes in and what CPU we are executing on.
The default is: service-time 0
path_grouping_policy
The default path grouping policy to apply to unspecified multipaths. Possible values
are:
failover One path per priority group.
multibus All paths in one priority group.
group_by_serial
One priority group per serial number.
group_by_prio
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.
group_by_node_name
One priority group per target node name. Target node names are fetched in
/sys/class/fc_transport/target*/node_name.
The default is: failover
uid_attrs Setting this option activates merging uevents by WWID, which may improve uevent
processing effiency. Moreover, it's 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 (e.g. sd:ATTR matches
sda), and ATTR is the name of the udev property to use for matching devices.
If this option is configured and matches the device node name of a device, it overrides
any other configured methods for determining the WWID for this device.
The default is: <unset>. To enable uevent merging, set it e.g. to "sd:ID_SERIAL
dasd:ID_UID nvme:ID_WWN".
uid_attribute The udev attribute providing a unique path identifier (WWID). If uid_attribute is set to
the empty string, WWID determination is done using the sysfs method rather then using
udev (not recommended in production; see WWID generation below).
The default is: ID_SERIAL, for SCSI devices
The default is: ID_UID, for DASD devices
The default is: ID_WWN, for NVMe devices
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.
The default is: <unset>
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:
const Return a constant priority of 1.
sysfs Use the sysfs attributes access_state and preferred_path to generate the
path priority. This prioritizer accepts the optional prio_arg
exclusive_pref_bit.
emc (Hardware-dependent) Generate the path priority for DGC class arrays as
CLARiiON CX/AX and EMC VNX and Unity families.
alua (Hardware-dependent) Generate the path priority based on the SCSI-3 ALUA
settings. This prioritizer accepts the optional prio_arg exclusive_pref_bit.
ontap (Hardware-dependent) Generate the path priority for NetApp ONTAP class and
OEM arrays as IBM NSeries.
rdac (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.
hp_sw (Hardware-dependent) Generate the path priority for HP/COMPAQ/DEC HSG80 and
MSA/HSV arrays with Active/Standby mode exclusively.
hds (Hardware-dependent) Generate the path priority for Hitachi AMS families of
arrays other than AMS 2000.
random Generate a random priority between 1 and 10.
weightedpath
Generate the path priority based on the regular expression and the priority
provided as argument. Requires prio_args keyword.
path_latency
Generate the path priority based on a latency algorithm. Requires prio_args
keyword.
ana (Hardware-dependent) Generate the path priority based on the NVMe ANA
settings.
datacore (Hardware-dependent) Generate the path priority for some DataCore storage
arrays. Requires prio_args keyword.
iet (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.
prio_args Arguments to pass to to the prio function. This only applies to certain prioritizers:
weighted Needs a value of the form "<hbtl|devname|serial|wwn> <regex1> <prio1>
<regex2> <prio2> ..."
hbtl Regex can be of SCSI H:B:T:L format. For example: 1:0:.:. , *:0:0:.
devname Regex can be of device name format. For example: sda , sd.e
serial 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
wwn 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:.*
path_latency
Needs a value of the form "io_num=<20> base_num=<10>"
io_num The number of read IOs sent to the current path continuously, used
to calculate the average path latency. Valid Values: Integer, [2,
200].
base_num
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.
alua If exclusive_pref_bit is set, paths with the preferred path bit set will
always be in their own path group.
sysfs If exclusive_pref_bit is set, paths with the preferred path bit set will
always be in their own path group.
datacore
preferredsds
(Mandatory) The preferred "SDS name".
timeout (Optional) The timeout for the INQUIRY, in ms.
iet
preferredip=...
(Mandatory) Th preferred IP address, in dotted decimal notation, for
iSCSI targets.
The default is: <unset>
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:
queue_if_no_path
(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.
pg_init_retries <times>
(Since kernel 2.6.24) Number of times to retry pg_init, it must be between 1
and 50.
pg_init_delay_msecs <msecs>
(Since kernel 2.6.38) Number of msecs before pg_init retry, it must be
between 0 and 60000.
queue_mode <mode>
(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 is: <unset>
path_checker The default method used to determine the path's state. The synchronous checkers (all
except tur and directio) will cause multipathd to pause most activity, waiting up to
checker_timeout seconds for the path to respond. The asynchronous checkers (tur and
directio) will not pause multipathd. Instead, multipathd will check for a response once
per second, until checker_timeout seconds have elapsed. Possible values are:
readsector0 (Deprecated) Read the first sector of the device. This checker is being
deprecated, please use tur instead.
tur Issue a TEST UNIT READY command to the device.
emc_clariion
(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.
hp_sw (Hardware-dependent) Check the path state for HP/COMPAQ/DEC HSG80 and
MSA/HSV arrays with Active/Standby mode exclusively.
rdac (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.
directio Read the first sector with direct I/O. This checker could cause spurious
path failures under high load. Increasing checker_timeout can help with
this.
cciss_tur (Hardware-dependent) Check the path state for HP/COMPAQ Smart Array(CCISS)
controllers.
none Do not check the device, fallback to use the values retrieved from sysfs
The default is: tur
alias_prefix The user_friendly_names prefix.
The default is: mpath
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.
immediate Immediately failback to the highest priority pathgroup that contains active
paths.
manual Do not perform automatic failback.
followover 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.
values > 0 Deferred failback (time to defer in seconds).
The default is: manual
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.
The default is: 1000
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.
The default is: 1
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.
The default is: max
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.
The default is: uniform
no_path_retry Specify what to do when all paths are down. Possible values are:
value > 0 Number of retries until disable I/O queueing.
fail For immediate failure (no I/O queueing).
queue For never stop I/O queueing, similar to queue_if_no_path. See KNOWN ISSUES.
The default is: fail
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.
The default is: no
checker_timeout Specify the timeout to use for path checkers and prioritizers, in seconds. Only
prioritizers that issue scsi commands use checker_timeout. If a path does not respond
to the checker command after checker_timeout seconds have elapsed, it is considered
down.
The default is: in /sys/block/<dev>/device/timeout
allow_usb_devices
If set to no , all USB devices will be skipped during path discovery. If you intend to
use multipath on USB attached devices, set this to yes.
The default is: no
flush_on_last_del
If set to yes , multipathd will disable queueing when the last path to a device has been
deleted.
The default is: no
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.
The default is: no
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.
The default is: 5
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.
The default is: 600
eh_deadline Specify the maximum number of seconds the SCSI layer will spend doing error handling
when scsi devices fail. After this timeout the scsi layer will perform a full HBA reset.
Setting this may be necessary in cases where the rport is never lost, so
fast_io_fail_tmo and dev_loss_tmo will never trigger, but (frequently do to load) scsi
commands still hang. Note: when the scsi error handler performs the HBA reset, all
target paths on that HBA will be affected. eh_deadline should only be set in cases where
all targets on the affected HBAs are multipathed.
The default is: <unset>
bindings_file This option is deprecated, and will be removed in a future release. The full pathname
of the binding file to be used when the user_friendly_names option is set.
The default is: /etc/multipath/bindings
wwids_file This option is deprecated, and will be removed in a future release. 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 default is: /etc/multipath/wwids
prkeys_file This option is deprecated, and will be removed in a future release. 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.
The default is: /etc/multipath/prkeys
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.
The default is: always
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.
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.
The default is: <unset>
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
The default is: no
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.
The default is: yes
Important Note: Linux kernel 4.3 or newer always behaves as if
"retain_attached_hw_handler yes" was set.
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.
The default is: yes
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.
The default is: yes
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.
The default is: no
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.
The default is: no
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.
The default is: no
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.
The default is: <unset>
config_dir This option is deprecated, and will be removed in a future release. 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.
The default is: /etc/multipath/conf.d/
san_path_err_threshold
If set to a value greater than 0, multipathd will watch paths and check how many times a
path has been failed due to errors.If the number of failures on a particular path is
greater then the san_path_err_threshold, then the path will not reinstate till
san_path_err_recovery_time. These path failures should occur within a
san_path_err_forget_rate checks, if not we will consider the path is good enough to
reinstantate. See "Shaky paths detection" below.
The default is: no
san_path_err_forget_rate
If set to a value greater than 0, multipathd will check whether the path failures has
exceeded the san_path_err_threshold within this many checks i.e
san_path_err_forget_rate . If so we will not reinstante the path till
san_path_err_recovery_time. See "Shaky paths detection" below.
The default is: no
san_path_err_recovery_time
If set to a value greater than 0, multipathd will make sure that when path failures has
exceeded the san_path_err_threshold within san_path_err_forget_rate then the path will
be placed in failed state for san_path_err_recovery_time duration.Once
san_path_err_recovery_time has timeout we will reinstante the failed path .
san_path_err_recovery_time value should be in secs. See "Shaky paths detection" below.
The default is: no
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. See "Shaky paths detection"
below.
The default is: no
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. See "Shaky paths
detection" below.
The default is: no
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. See
"Shaky paths detection" below.
The default is: no
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. See "Shaky paths
detection" below.
The default is: no
delay_watch_checks
This option is deprecated, and mapped to san_path_err_forget_rate. If this is set to a
value greater than 0 and no san_path_err options are set, san_path_err_forget_rate will
be set to the value of delay_watch_checks and san_path_err_threshold will be set to 1.
See the san_path_err_forget_rate and san_path_err_threshold options, and "Shaky paths
detection" below for more information.
The default is: no
delay_wait_checks
This option is deprecated, and mapped to san_path_err_recovery_time. If this is set to
a value greater than 0 and no san_path_err options are set, san_path_err_recovery_time
will be set to the value of delay_wait_checks times max_polling_interval. This will give
approximately the same wait time as delay_wait_checks previously did. Also,
san_path_err_threshold will be set to 1. See the san_path_err_recovery_time and
san_path_err_threshold options, and "Shaky paths detection" below for more information.
The default is: no
marginal_pathgroups
If set to no, the delay_*_checks, marginal_path_*, and san_path_err_* options will keep
marginal, or "shaky", paths from being reinstated until they have been monitored for
some time. This can cause situations where all non-marginal paths are down, and no paths
are usable until multipathd detects this and reinstates a marginal path. If the
multipath device is not configured to queue IO in this case, it can cause IO errors to
occur, even though there are marginal paths available. However, if this option is set
to yes, when one of the marginal path detecting methods determines that a path is
marginal, it will be reinstated and placed in a seperate pathgroup that will only be
used after all the non-marginal pathgroups have been tried first. This prevents the
possibility of IO errors occuring while marginal paths are still usable. After the path
has been monitored for the configured time, and is declared healthy, it will be returned
to its normal pathgroup. See "Shaky paths detection" below for more information.
The default is: no
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:
strict 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.
no Multipath behaves like strict. Multipathd behaves like greedy.
yes 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.
greedy Both multipathd and multipath treat every non-blacklisted device as multipath
device path.
smart 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.
The default is: strict
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.
The default is: -10 (10s for known and 1s for unknown hardware)
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.
The default is: 4000
retrigger_tries Sets the number of times multipathd will try to retrigger a uevent to get the WWID.
The default is: 3
retrigger_delay Sets the amount of time, in seconds, to wait between retriggers.
The default is: 10
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.
The default is: 30
skip_kpartx If set to yes , kpartx will not automatically create partitions on the device.
The default is: no
disable_changed_wwids
This option is deprecated and ignored. If the WWID of a path suddenly changes,
multipathd handles it as if it was removed and then added again.
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.
The default is: 0
max_sectors_kb Sets the max_sectors_kb device parameter on all path devices and the multipath device to
the specified value.
The default is: in /sys/block/<dev>/queue/max_sectors_kb
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 no makes multipath immediately mark a device with only
ghost paths as ready.
The default is: no
enable_foreign Enables or disables foreign libraries (see section FOREIGN MULTIPATH SUPPORT below). The
value is a regular expression; foreign libraries are loaded if their name (e.g. "nvme")
matches the expression. By default, no foreign libraries are enabled. Set this to "nvme"
to enable NVMe native multipath support, or ".*" to enable all foreign libraries.
The default is: "NONE"
recheck_wwid If set to yes, when a failed path is restored, its wwid is rechecked. If the wwid has
changed, the path is removed from the current multipath device, and re-added as a new
path. Multipathd will also recheck a path's wwid if it is manually re-added. This option
only works for SCSI devices that are configured to use the default uid_attribute,
ID_SERIAL, or sysfs for getting their wwid.
The default is: no
blacklist and blacklist_exceptions sections
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.
In the blacklist and blacklist_exceptions sections, starting a quoted value with an exclamation mark "!"
will invert the matching of the rest of the regular expression. For instance, "!^sd[a-z]" will match all
values that do not start with "sd[a-z]". The exclamation mark can be escaped "\!" to match a literal ! at
the start of a regular expression. Note: The exclamation mark must be inside quotes, otherwise it will be
treated as starting a comment.
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.
The default blacklist consists of the regular expression "!^(sd[a-z]|dasd[a-
z]|nvme[0-9])". This causes all device types other than scsi, dasd, and nvme to be
excluded from multipath handling by default.
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.
Note: The behavior of this option has changed in multipath-tools 0.8.2 compared to
previous versions. Blacklisting by missing properties is only applied to devices which
do have the property specified by uid_attribute (e.g. ID_SERIAL) set. Previously, it was
applied to every device, possibly causing devices to be blacklisted because of temporary
I/O error conditions.
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.
protocol 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.
multipaths section
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:
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:
path_grouping_policy
path_selector
prio
prio_args
failback
rr_weight
no_path_retry
rr_min_io
rr_min_io_rq
flush_on_last_del
features
reservation_key
user_friendly_names
deferred_remove
san_path_err_threshold
san_path_err_forget_rate
san_path_err_recovery_time
marginal_path_err_sample_time
marginal_path_err_rate_threshold
marginal_path_err_recheck_gap_time
marginal_path_double_failed_time
delay_watch_checks
delay_wait_checks
skip_kpartx
max_sectors_kb
ghost_delay
devices 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:
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".
vpd_vendor The vendor specific vpd page information, using the vpd page abbreviation. The vpd page
abbreviation can be found by running sg_vpd -e. multipathd will use this information to
gather device specific information that can be displayed with the %g wilcard for the
multipathd show maps format and multipathd show paths format commands. Currently only
the hp3par vpd page is supported.
hardware_handler 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.
1 ana (Hardware-dependent) Hardware handler for NVMe ANA 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:
path_grouping_policy
uid_attribute
getuid_callout
path_selector
path_checker
prio
prio_args
features
failback
rr_weight
no_path_retry
rr_min_io
rr_min_io_rq
fast_io_fail_tmo
dev_loss_tmo
flush_on_last_del
user_friendly_names
retain_attached_hw_handler
detect_prio
detect_checker
deferred_remove
san_path_err_threshold
san_path_err_forget_rate
san_path_err_recovery_time
marginal_path_err_sample_time
marginal_path_err_rate_threshold
marginal_path_err_recheck_gap_time
marginal_path_double_failed_time
delay_watch_checks
delay_wait_checks
skip_kpartx
max_sectors_kb
ghost_delay
all_tg_pt
overrides section
The overrides section recognizes the following optional attributes; if not set the values are taken from
the devices or defaults sections:
path_grouping_policy
uid_attribute
getuid_callout
path_selector
path_checker
alias_prefix
features
prio
prio_args
failback
rr_weight
no_path_retry
rr_min_io
rr_min_io_rq
flush_on_last_del
fast_io_fail_tmo
dev_loss_tmo
user_friendly_names
retain_attached_hw_handler
detect_prio
detect_checker
deferred_remove
san_path_err_threshold
san_path_err_forget_rate
san_path_err_recovery_time
marginal_path_err_sample_time
marginal_path_err_rate_threshold
marginal_path_err_recheck_gap_time
marginal_path_double_failed_time
delay_watch_checks
delay_wait_checks
skip_kpartx
max_sectors_kb
ghost_delay
all_tg_pt
WWID generation
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):
uid_attrs The WWID is derived from udev attributes by matching the device node name; cf uid_attrs
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.
sysfs Try to determine the WWID from sysfs attributes. For SCSI devices, this means reading
the Vital Product Data (VPD) page "Device Identification" (0x83).
The default settings (using udev and uid_attribute configured from the built-in hardware table) should
work fine in most scenarios. Users who want to enable uevent merging must set uid_attrs.
Shaky paths detection
A common problem in SAN setups is the occurence of intermittent errors: a path is unreachable, then
reachable again for a short time, disappears again, and so forth. This happens typically on unstable
interconnects. It is undesirable to switch pathgroups unnecessarily on such frequent, unreliable events.
multipathd supports three different methods for detecting this situation and dealing with it. All methods
share the same basic mode of operation: If a path is found to be "shaky" or "flipping", and appears to be
in healthy status, it is not reinstated (put back to use) immediately. Instead, it is placed in the
"delayed" state and watched for some time, and only reinstated if the healthy state appears to be stable.
If the marginal_pathgroups option is set, the path will reinstated immediately, but placed in a special
pathgroup for marginal paths. Marginal pathgroups will not be used until all other pathgroups have been
tried. At the time when the path would normally be reinstated, it will be returned to its normal
pathgroup. The logic of determining "shaky" condition, as well as the logic when to reinstate, differs
between the three methods.
"delay_checks" failure tracking
This method is deprecated and mapped to the "san_path_err" method. See the delay_watch_checks
and delay_wait_checks options above for more information.
"marginal_path" failure tracking
If a second failure event (good->bad transition) occurs within marginal_path_double_failed_time
seconds after a failure, high-frequency monitoring is started for the affected path: I/O is sent
at a rate of 10 per second. This is done for marginal_path_err_sample_time seconds. During this
period, the path is not reinstated. If the rate of errors remains below
marginal_path_err_rate_threshold during the monitoring period, the path is reinstated. Otherwise,
it is kept in failed state for marginal_path_err_recheck_gap_time, and after that, it is
monitored again. For this method, time intervals are measured in seconds.
"san_path_err" failure tracking
multipathd counts path failures for each path. Once the number of failures exceeds the value
given by san_path_err_threshold, the path is not reinstated for san_path_err_recovery_time
seconds. While counting failures, multipathd "forgets" one past failure every
"san_path_err_forget_rate" ticks; thus if errors don't occur more often then once in the forget
rate interval, the failure count doesn't increase and the threshold is never reached. Ticks are
the time between path checks by multipathd, which is variable and controlled by the
polling_interval and max_polling_interval parameters.
This method is deprecated in favor of the "marginal_path" failure tracking method, and only
offered for backward compatibility.
See the documentation of the individual options above for details. It is strongly discouraged to use
more than one of these methods for any given multipath map, because the two concurrent methods may
interact in unpredictable ways. If the "marginal_path" method is active, the "san_path_err" parameters
are implicitly set to 0.
FOREIGN MULTIPATH SUPPORT
multipath and multipathd can load "foreign" libraries to add support for other multipathing technologies
besides the Linux device mapper. Currently this support is limited to printing detected information
about multipath setup. In topology output, the names of foreign maps are prefixed by the foreign library
name in square brackets, as in this example:
# multipath -ll
uuid.fedcba98-3579-4567-8765-123456789abc [nvme]:nvme4n9 NVMe,Some NVMe controller,FFFFFFFF
size=167772160 features='n/a' hwhandler='ANA' wp=rw
|-+- policy='n/a' prio=50 status=optimized
| `- 4:38:1 nvme4c38n1 0:0 n/a optimized live
`-+- policy='n/a' prio=50 status=optimized
`- 4:39:1 nvme4c39n1 0:0 n/a optimized live
The "nvme" foreign library provides support for NVMe native multipathing in the kernel. It is part of the
standard multipath package.
KNOWN ISSUES
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.
SEE ALSO
udev(8), dmsetup(8), multipath(8), multipathd(8).
AUTHORS
multipath-tools was developed by Christophe Varoqui, <christophe.varoqui@opensvc.com> and others.