4.4. Multipaths Device Configuration Attributes
4.4. Multipaths Device Configuration Attributes Table 4.2, "Multipath Attributes" shows the attributes that you can set in the multipaths section of the multipath.conf configuration file for each specific multipath device. These attributes apply only to the one specified multipath. These defaults are used by DM-Multipath and override attributes set in the defaults and devices sections of the multipath.conf file. Table 4.2. Multipath Attributes Attribute Description wwid Specifies the WWID of the multipath device to which the multipath attributes apply. This parameter is mandatory for this section of the multipath.conf file. alias Specifies the symbolic name for the multipath device to which the multipath attributes apply. If you are using user_friendly_names , do not set this value to mpath n ; this may conflict with an automatically assigned user friendly name and give you incorrect device node names. path_grouping_policy Specifies the default path grouping policy to apply to unspecified multipaths. Possible values include: failover = 1 path per priority group multibus = all valid paths in 1 priority group group_by_serial = 1 priority group per detected serial number group_by_prio = 1 priority group per path priority value group_by_node_name = 1 priority group per target node name path_selector Specifies the default algorithm to use in determining what path to use for the I/O operation. Possible values include: round-robin 0 : Loop through every path in the path group, sending the same amount of I/O to each. queue-length 0 : Send the bunch of I/O down the path with the least number of outstanding I/O requests. service-time 0 : Send the bunch of I/O down the path with the shortest estimated service time, which is determined by dividing the total size of the outstanding I/O to each path by its relative throughput. failback Manages path group failback. A value of immediate specifies immediate failback to the highest priority path group that contains active paths. A value of manual specifies that there should not be immediate failback but that failback can happen only with operator intervention. A value of followover specifies that automatic failback should be performed when the first path of a path group becomes active. This keeps a node from automatically failing back when another node requested the failover. A numeric value greater than zero specifies deferred failback, expressed in seconds. prio Specifies the default function to call to obtain a path priority value. For example, the ALUA bits in SPC-3 provide an exploitable prio value. Possible values include: const : Set a priority of 1 to all paths. emc : Generate the path priority for EMC arrays. alua : Generate the path priority based on the SCSI-3 ALUA settings. As of Red Hat Enterprise Linux 6.8, if you specify prio "alua exclusive_pref_bit" in your device configuration, multipath will create a path group that contains only the path with the pref bit set and will give that path group the highest priority. tpg_pref : Generate the path priority based on the SCSI-3 ALUA settings, using the preferred port bit. ontap : Generate the path priority for NetApp arrays. rdac : Generate the path priority for LSI/Engenio 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. no_path_retry A numeric value for this attribute specifies the number of times the system should attempt to use a failed path before disabling queuing. A value of fail indicates immediate failure, without queuing. A value of queue indicates that queuing should not stop until the path is fixed. rr_min_io Specifies the number of I/O requests to route to a path before switching to the path in the current path group. This setting is only for systems running kernels older that 2.6.31. Newer systems should use rr_min_io_rq . The default value is 1000. rr_min_io_rq Specifies the number of I/O requests to route to a path before switching to the path in the current path group, using request-based device-mapper-multipath. This setting should be used on systems running current kernels. On systems running kernels older than 2.6.31, use rr_min_io . The default value is 1. rr_weight If set to priorities , then instead of sending rr_min_io requests to a path before calling path_selector to choose the path, the number of requests to send is determined by rr_min_io times the path's priority, as determined by the prio function. If set to uniform , all path weights are equal. flush_on_last_del If set to yes , then multipath will disable queuing when the last path to a device has been deleted. user_friendly_names If set to yes , specifies that the system should use the /etc/multipath/bindings file to assign a persistent and unique alias to the multipath, in the form of mpath n . If set to no , specifies that the system should use use the WWID as the alias for the multipath. In either case, what is specified here will be overridden by any device-specific aliases you specify in the multipaths section of the configuration file. delay_watch_checks (Red Hat Enterprise Linux Release 6.7 and later) If set to a value greater than 0, the multipathd daemon will watch paths that have recently become valid for the specified number of checks. If they fail again while they are being watched, when they become valid they will not be used until they have stayed up for the number of consecutive checks specified with delay_wait_checks . This allows you to keep paths that may be unreliable from immediately being put back into use as soon as they come back online. delay_wait_checks (Red Hat Enterprise Linux Release 6.7 and later) If set to a value greater than 0, when a device that has recently come back online fails again within the number of checks specified with delay_watch_checks , the time it comes back online it will be marked and delayed and it will not be used until it has passed the number of checks specified in delay_wait_checks . skip_kpartx (Red Hat Enterprise Linux Release 6.9 and later) If set to yes , kpartx will not automatically create partitions on the device. This allows users to create a multipath device without creating partitions, even if the device has a partition table. max_sectors_kb (Red Hat Enterprise Linux Release 6.9 and later) Sets the max_sectors_kb device queue parameter to the specified value on all underlying paths of a multipath device before the multipath device is first activated. When a multipath device is created, the device inherits the max_sectors_kb value from the path devices. Manually raising this value for the multipath device or lowering this value for the path devices can cause multipath to create I/O operations larger than the path devices allow. Using the max_sectors_kb parameter is an easy way to set these values before a multipath device is created on top of the path devices and prevent invalid-sized I/O operations from being passed If this parameter is not set by the user, the path devices have it set by their device driver, and the multipath device inherits it from the path devices. The following example shows multipath attributes specified in the configuration file for two specific multipath devices. The first device has a WWID of 3600508b4000156d70001200000b0000 and a symbolic name of yellow . The second multipath device in the example has a WWID of 1DEC_____321816758474 and a symbolic name of red . In this example, the rr_weight attributes is set to priorities .
multipaths { multipath { wwid 3600508b4000156d70001200000b0000 alias yellow path_grouping_policy multibus path_selector "round-robin 0" failback manual rr_weight priorities no_path_retry 5 } multipath { wwid 1DEC_____321816758474 alias red rr_weight priorities } }