MULTIPATH.CONF(5)						File Formats Manual						 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 occor.

       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; 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/tar-
				    get*/node_name.

			Default value is failover.

       uid_attribute	The udev attribute providing a unique path identifier. Default value is ID_SERIAL

       prio		The name of the path priority routine. The specified routine should return a numeric value specifying the relative  prior-
			ity of this path. Higher number have a higher priority.  none is a valid value. Currently the following path priority rou-
			tines 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 const.

       prio_args	Arguments  to pass to to the prio function.  Currently only used with weighted, which needs a value of the form <hbtl|dev-
			name> <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 multi-
			path. 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. Default is 0.

       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 spe-
			cific 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  fail-
			ing  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 remov-
			ing  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/multi-
			path/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 multi-
			path 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  persis-
			tent 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, mul-
			tipath 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

       hw_str_match	If set to yes , the vendor, product, and revision parameters of user device configs will be  string  matched  against  the
			built-in  device  configs  to  determine if they should modify an existing config, or create a new one. If set to no , the
			user device configs will be regular expression matched against the built-in configs instead. 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.

       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.

       devnode		Regular expression of the device nodes 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.

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_q
	      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.

								 30 November 2006						 MULTIPATH.CONF(5)