Provided by: multipath-tools_0.5.0+git1.656f8865-5ubuntu2.5_amd64 
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)