multipath.conf(5)
NAME
multipath.conf - multipath daemon configuration file
DESCRIPTION
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.
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.
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.
devices This section defines the device-specific settings.
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:
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. Default is 5
max_polling_interval
maximal interval between two path checks in seconds;
default is 4 * polling_interval
multipath_dir directory where the dynamic shared objects are stored;
default is system dependent, commonly /lib/multipath
find_multipaths If set to yes , instead of trying to create a
multipath device for every non-blacklisted path,
multipath will only create a device if one of three
condidions are met. 1 There are at least two non-
blacklisted paths with the same wwid, 2 the user
manually forces the creation, by specifying a device
with the multipath command, or 3 a path has the same
WWID as a multipath device that was previously created
while find_multipaths was set (even if that multipath
device doesn't currently exist). Whenever a multipath
device is created with find_multipaths set, multipath
will remeber the WWID of the device, so that it will
automatically create the device again, as soon as it
sees a path with that WWID. This should allow most
users to have multipath automatically choose the
correct paths to make into multipath devices, without
having to edit the blacklist; Default is no
verbosity default verbosity. Higher values increase the
verbosity level. Valid levels are between 0 and 6;
default is 2
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. Default is yes
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 IO to each.
queue-length 0
Send the next bunch of IO down the path
with the least amount of outstanding IO.
service-time 0
Choose the path for the next bunch of IO
based on the amount of outstanding IO to
the path and its relative throughput.
path_grouping_policy
The default path grouping policy to apply to
unspecified multipaths. Possible values are
failover 1 path per priority group
multibus all paths in 1 priority group
group_by_serial
1 priority group per serial number
group_by_prio
1 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
1 priority group per target node name.
Target node names are fetched in
/sys/class/fc_transport/target*/node_name.
Default value is failover.
uid_attribute The udev attribute providing a unique path identifier.
Default value is ID_SERIAL
getuid_callout The default program and args to callout to obtain a
unique path identifier. Should be specified with an
absolute path. This parameter is deprecated.
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.
emc Generate the path priority for EMC arrays.
alua Generate the path priority based on the
SCSI-3 ALUA settings.
ontap Generate the path priority for NetApp
arrays.
rdac Generate the path priority for
LSI/Engenio/NetApp E-Series RDAC
controller.
hp_sw Generate the path priority for Compaq/HP
controller in active/standby mode.
hds Generate the path priority for Hitachi HDS
Modular storage arrays.
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.
Default value is none.
prio_args Arguments to pass to to the prio function. Currently
only used with weighted, which needs a value of the
form <hbtl|devname> <regex1> <prio1> <regex2> <prio2>
... hbtl regex can be of SCSI H:B:T:L format Ex:
1:0:.:. , *:0:0:. devname regex can be of device name
format Ex: sda , sd.e
features Specify any device-mapper features to be used. Syntax
is num list where num is the number of features in
list. Possible values for the feature list are
queue_if_no_path
Queue IO if no path is active; identical
to the no_path_retry keyword.
no_partitions
Disable automatic partitions generation
via kpartx.
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 directio instead
tur Issue a TEST UNIT READY command to the
device.
emc_clariion
Query the EMC Clariion specific EVPD page
0xC0 to determine the path state.
hp_sw Check the path state for HP storage arrays
with Active/Standby firmware.
rdac Check the path state for
LSI/Engenio/NetApp E-Series RDAC storage
controller.
directio Read the first sector with direct I/O.
Default value is directio.
failback Tell multipathd how to manage path group failback.
immediate Immediately failback to the highest
priority pathgroup that contains active
paths.
manual Do not perform automatic failback.
followover Only perform automatic failback when the
first path of a pathgroup becomes active.
This keeps a node from automatically
failing back when another node requested
the failover.
values > 0 deferred failback (time to defer in
seconds)
Default value is manual.
rr_min_io The number of IO to route to a path before switching
to the next in the same path group. This is only for
BIO based multipath. Default is 1000
rr_min_io_rq The number of IO requests to route to a path before
switching to the next in the same path group. This is
only for request based multipath. Default is 1
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. Default is
uniform.
no_path_retry Specify the number of retries until disable queueing,
or fail for immediate failure (no queueing), queue for
never stop queueing. If unset no queueing is
attempted. Default is unset.
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. Default is no
flush_on_last_del
If set to yes , multipathd will disable queueing when
the last path to a device has been deleted. Default is
no
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.
checker_timeout Specify the timeout to use for path checkers and
prioritizers that issue scsi commands with an explicit
timeout, in seconds; default taken from
/sys/block/sd<x>/device/timeout
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 IO to devices on that remote port.
This should be smaller than dev_loss_tmo. Setting this
to off will disable the timeout.
dev_loss_tmo Specify the number of seconds the scsi layer will wait
after a problem has been detected on a FC remote port
before removing it from the system. This can be set to
"infinity" which sets it to the max value of
2147483647 seconds, or 68 years. It will be
automatically adjusted to the overall retry interval
no_path_retry * polling_interval if a number of
retries is given with no_path_retry and the overall
retry interval is longer than the specified
dev_loss_tmo value. The linux kernel will cap this
value to 300 if fast_io_fail_tmo is not set.
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 IO 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 IO. Setting queue_without_daemon to no ,
avoids this problem. Default is yes
bindings_file The full pathname of the binding file to be used when
the user_friendly_names option is set. Defaults to
/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. Defaults to
/etc/multipath/wwids
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. 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. It is
unset by default.
retain_attached_hw_handler
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. Default is no
detect_prio If set to yes , multipath will try to detect if the
device supports ALUA. If so, the device will
automatically use the alua prioritizer. If not, the
prioritizer will be selected as usual. Default is no
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
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. Default is no
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. Default is /etc/multipath/conf.d
delay_watch_checks
If set to a value greater than 0, multipathd will
watch paths that have recently become valid for this
many checks. If they fail again while they are being
watched, when they next become valid, they will not be
used until they have stayed up for delay_wait_checks
checks. Default is no
delay_wait_checks
If set to a value greater than 0, when a device that
has recently come back online fails again within
delay_watch_checks checks, the next time it comes back
online, it will marked and delayed, and not used until
it has passed delay_wait_checks checks. Default is no
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 In these
cases it is recommended to increase the CLI timeout to
avoid those issues. The default is 1000
blacklist section
The blacklist section is used to exclude specific device from inclusion
in the multipath topology. It is most commonly used to exclude local
disks or LUNs for the array controller.
The following keywords are recognized:
wwid The World Wide Identification of a device.
devnode Regular expression of the device nodes to be excluded.
property Regular expression of the udev property to be
excluded.
device Subsection for the device description. This subsection
recognizes the vendor and product keywords. For a full
description of these keywords please see the devices
section description.
blacklist_exceptions section
The blacklist_exceptions section is used to revert the actions of the
blacklist section, ie to include specific device in the multipath
topology. This allows one to selectively include devices which would
normally be excluded via the blacklist section.
The following keywords are recognized:
wwid The World Wide Identification of a device.
property Regular expression of the udev property to be
whitelisted. Defaults to (ID_WWN|SCSI_IDENT_.*)
devnode Regular expression of the device nodes to be
whitelisted.
device Subsection for the device description. This subsection
recognizes the vendor and product keywords. For a full
description of these keywords please see the devices
section description.
The property blacklist and whitelist handling is different from the
usual handling in the sense that the whitelist has to be set, otherwise
the device will be blacklisted. In these cases the message
blacklisted, udev property missing will be displayed.
multipaths section
The only recognized attribute for the multipaths section is the
multipath subsection.
The multipath subsection recognizes the following attributes:
wwid Index of the container. Mandatory for this subsection.
alias (Optional) symbolic name for the multipath map.
The following attributes are optional; if not set the default values
are taken from the defaults or devices section:
path_grouping_policy
path_selector
prio
prio_args
failback
rr_weight
flush_on_last_del
no_path_retry
rr_min_io
rr_min_io_rq
features
reservation_key
deferred_remove
delay_watch_checks
delay_wait_checks
devices section
The only recognized attribute for the devices section is the device
subsection.
The device subsection recognizes the following attributes:
vendor (Mandatory) Vendor identifier
product (Mandatory) Product identifier
revision (Optional) Revision identfier
product_blacklist
(Optional) Product strings to blacklist for this
vendor
alias_prefix (Optional) The user_friendly_names prefix to use for
this device type, instead of the default "mpath"
hardware_handler (Optional) The hardware handler to use for this device
type. The following hardware handler are implemented:
1 emc Hardware handler for EMC storage arrays.
1 rdac Hardware handler for LSI/Engenio/NetApp E-
Series RDAC storage controller.
1 hp_sw Hardware handler for Compaq/HP storage
arrays in active/standby mode.
1 alua Hardware handler for SCSI-3 ALUA
compatible arrays.
The following attributes are optional; if not set the default values
are taken from the defaults section:
path_grouping_policy
uid_attribute
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
retain_attached_hw_handler
detect_prio
deferred_remove
delay_watch_checks
delay_wait_checks
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
deferred_remove
delay_watch_checks
delay_wait_checks
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 three methods (in the order of preference):
getuid_callout Use the specified external program; cf getuid_callout
above. Care should be taken when using this method;
the external program needs to be loaded from disk for
execution, which might lead to deadlock situations in
an all-paths-down scenario.
uid_attribute Use the value of the specified udev attribute; cf
uid_attribute above. This method is preferred to
getuid_callout as multipath does not need to call any
external programs here. However, under certain
circumstances udev might not be able to generate the
requested variable.
vpd_pg83 If none of the getuid_callout or uid_attribute
parameters are present multipath will try to use the
sysfs attribute vpd_pg83 to generate the wwid.
KNOWN ISSUES
The 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 was developed by Christophe Varoqui,
<christophe.varoqui@opensvc.com> and others.
30 November 2006 MULTIPATH.CONF(5)
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