Provided by: multipath-tools_0.8.3-1ubuntu2.3_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 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 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 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 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 (Deprecated) Read the first sector with direct I/O. This
checker is being deprecated, it could cause spurious path
failures under high load. Please use tur instead.
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 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/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
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 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 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: 1000
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: <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 active ones. Setting this
to 0 or on 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,
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 multipath topology. It
is most commonly used to exclude local disks or non-disk devices (such as LUNs for the
storage array controller) from being handled by multipath-tools.
The blacklist_exceptions section is used to revert the actions of the blacklist section.
This allows one to selectively include ("whitelist") devices which would normally be
excluded via the blacklist section. A common usage is to blacklist "everything" using a
catch-all regular expression, and create specific blacklist_exceptions entries for those
devices that should be handled by multipath-tools.
The following keywords are recognized in both sections. The defaults are empty unless
explicitly stated.
devnode Regular expression matching the device nodes to be excluded/included.
The default blacklist consists of the regular expressions
"^(ram|zram|raw|loop|fd|md|dm-|sr|scd|st|dcssblk)[0-9]" and
"^(td|hd|vd)[a-z]". This causes virtual devices, non-disk devices, and
some other device types to be excluded from multipath handling by
default.
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".
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.