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> {
}
}
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), which is taken to be the value of the
udev attribute given by the uid_attribute keyword.
- devices
- This section defines the device-specific settings.
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
- 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; uid_attribute should be used instead.
- 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 user for path checkers 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
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|ID_SCSI_VPD)
- 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
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
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.