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MULTIPATH.CONF(5) File Formats Manual MULTIPATH.CONF(5)

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 mul-
tipath -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 recog-
nized 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 consecu-
tive 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 at-
tribute 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 ap-
propriate 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 de-
tails on the WWID generation see section WWID genera-
tion below. Attributes set in this section take prece-
dence over all others.

devices This section defines the device-specific settings. De-
vices 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 ver-
bosity level. Valid levels are between 0 and 6.

The default is: 2

polling_interval Interval between two path checks in seconds. For prop-
erly 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 un-
derlying block devices. Possible values are yes and
no.

The default is: no

multipath_dir 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. There are
three selector algorithms:

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.

The default is: service-time 0

path_grouping_policy
The default path grouping policy to apply to unspeci-
fied 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 pro-
grams specified as a global, per-con-
troller 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. More-
over, it's an alternative method to configure the udev
properties to use for determining unique path identi-
fiers (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 config-
ured methods for determining the WWID for this de-
vice.

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 prior-
ity. 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 set-
tings. This prioritizer accepts the op-
tional 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 ar-
rays 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 pro-
vided as argument. Requires prio_args key-
word.

path_latency
Generate the path priority based on a la-
tency algorithm. Requires prio_args key-
word.

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. Re-
quires prio_args keyword.

The default depends on the detect_prio setting: If de-
tect_prio is yes (default), the default priority algo-
rithm 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|dev-
name|serial|wwn_ _regex1_ _prio1_ _regex2_
_prio2_ ..."

hbtl Regex can be of SCSI H:B:T:L for-
mat. For example: 1:0:.:. ,
*:0:0:.

devname Regex can be of device name for-
mat. For example: sda , sd.e

serial Regex can be of serial number for-
mat. For example: .*J1FR.*324 .
The serial can be looked up
through sysfs or by running multi-
pathd show paths format "%z". For
example: 0395J1FR904324

wwn Regex can be of the form
"host_wwnn:host_wwpn:tar-
get_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.red-
hat.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 la-
tency. Valid Values: Integer, [2,
200].

base_num
The base number value of logarith-
mic scale, used to partition dif-
ferent priority ranks. Valid Val-
ues: Integer, [2, 10]. And Max av-
erage 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 IN-
QUIRY, in ms.

iet

preferredip=...
(Mandatory) Th preferred IP ad-
dress, 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 be-
fore 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 paths state.
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 de-
vice.

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 Ne-
tApp SANtricity E/EF Series, and OEM ar-
rays from IBM DELL SGI STK and SUN.

directio (Deprecated) Read the first sector with
direct I/O. This checker is being depre-
cated, it could cause spurious path fail-
ures under high load. Please use tur in-
stead.

cciss_tur (Hardware-dependent) Check the path state
for HP/COMPAQ Smart Array(CCISS) con-
trollers.

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 prior-
ity pathgroup that contains active paths.

manual Do not perform automatic failback.

followover Used to deal with multiple computers ac-
cessing 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 au-
tomatically failing back when another node
requested the failover.

values _ 0 Deferred failback (time to defer in sec-
onds).

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". Possi-
ble 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 queue-
ing.

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 de-
vices that set no_path_retry. If a machine is shut
down while all paths to a device are down, it is pos-
sible to hang waiting for I/O to return from the de-
vice after multipathd has been stopped. Without multi-
pathd 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 prob-
lem.

The default is: no

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

The default is: in /sys/block/sd<x>/device/timeout

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/multi-
path/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 mul-
tipaths 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 automati-
cally adjusted to the overall retry interval
no_path_retry * polling_interval if a number of re-
tries 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

bindings_file 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 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 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 pro-
vided 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 re-
moved from the prkeys_file. The prkeys file will auto-
matically 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 mpath-
persist on these arrays. Setting this option is iden-
tical 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 be-
haves 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 re-
quired 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 sec-
onds. On busy systems path checks might take longer
than one second; here the missing ticks will be ac-
counted for on the next round. A warning will be
printed if path checks take longer than polling_inter-
val 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 de-
vice before the last user closes it, the deferred re-
move 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 mul-
tipath 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 in-
serts that string between device name and partition
number to construct the partition device name. Other-
wise (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 de-
fault value for this option; in this case, the user
must set it to "/UNSET/" to obtain the original <un-
set> behavior. Use multipath -T to check the current
settings.

The default is: <unset>

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 di-
rectory 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 rein-
state till san_path_err_recovery_time. These path
failures should occur within a san_path_err_for-
get_rate checks, if not we will consider the path is
good enough to reinstantate. See "Shaky paths detec-
tion" 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 rein-
stante 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 rein-
stante 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 er-
ror. When a path failed event occurs twice in mar-
ginal_path_double_failed_time seconds due to an IO er-
ror and all the other three parameters are set, multi-
pathd 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 er-
ror. If it is set to a value no less than 120, when a
path fail event occurs twice in marginal_path_dou-
ble_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 di-
rect 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 mar-
ginal_path_err_recheck_gap_time seconds unless there
is only one active path. After mar-
ginal_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. Re-
fer 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 mar-
ginal_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 er-
ror. 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 mar-
ginal_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 ex-
pires, the path will be requeueed for checking. If
checking result is good enough, the path will be rein-
stated, 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 de-
tection" 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 de-
lay_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 moni-
tored for some time. This can cause situations where
all non-marginal paths are down, and no paths are us-
able until multipathd detects this and reinstates a
marginal path. If the multipath device is not config-
ured to queue IO in this case, it can cause IO errors
to occur, even though there are marginal paths avail-
able. 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 de-
clared 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 de-
vices they encounter. This matters a) when a device is
encountered by multipath -u during udev rule process-
ing (a device is blocked from further processing by
higher layers - such as LVM - if and only if it's con-
sidered 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 multi-
path maps using the multipathd add map com-
mand. Once set up manually, the map is re-
membered 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 set-
ting up the map fails, a new uevent is trig-
gered for the device; at second encounter in
the udev rules, the device will be treated
as non-multipath and passed on to upper lay-
ers. Note: this may cause delays during de-
vice detection if there are single-path de-
vices which aren't blacklisted.

The default is: strict

find_multipaths_timeout
Timeout, in seconds, to wait for additional paths af-
ter 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 (recom-
mended), 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 ("un-
known") 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 sys-
tems 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: 1000

retrigger_tries Sets the number of times multipathd will try to re-
trigger 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, multi-
path 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: <device dependent>

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 ac-
tive ones. Setting this to 0 or on makes multipath im-
mediately 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 regu-
lar expression; foreign libraries are loaded if their
name (e.g. "nvme") matches the expression. By default,
all foreign libraries are enabled.

The default is: "" (the empty regular expression)

blacklist and blacklist_exceptions sections
The blacklist section is used to exclude specific devices from the mul-
tipath 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 ex-
pression, 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 ex-
cluded/included.

The default blacklist consists of the regular expres-
sions "^(ram|zram|raw|loop|fd|md|dm-|sr|scd|st|dcss-
blk)[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.

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 ex-
cluded/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 mul-
tipath-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 condi-
tions.

The default blacklist exception is:
(SCSI_IDENT_|ID_WWN), causing well-behaved SCSI de-
vices and devices that provide a WWN (World Wide Num-
ber) 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 de-
vice 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 multi-
path 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 prece-
dence over a an entry for the same WWID in the bind-
ings_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 un-
der config_dir (in reverse alphabetical order) have the highest prece-
dence, followed by entries in multipath.conf; the built-in hardware ta-
ble has the lowest precedence. Inside a configuration file, later en-
tries 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 de-
vice 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 de-
vices, 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:

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 automati-
cally attach a device handler to known devices (which
includes all devices supporting SCSI-3 ALUA) and dis-
allow changing the handler afterwards. Setting hard-
ware_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 ge-
tuid_callout as multipath does not need to call any
external programs here. However, under certain circum-
stances udev might not be able to generate the re-
quested 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, disap-
pears again, and so forth. This happens typically on unstable intercon-
nects. It is undesirable to switch pathgroups unnecessarily on such
frequent, unreliable events. multipathd supports three different meth-
ods 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 nor-
mally 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 op-
tions 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 mar-
ginal_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 sec-
onds. 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" fail-
ure tracking method, and only offered for backward compatibil-
ity.

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 multi-
pathing 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 be-
ing 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 set-
ting accordingly to avoid this deadlock. Hence if both values are spec-
ified 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.varo-
qui@opensvc.com> and others.

Linux 2018-05-21 MULTIPATH.CONF(5)