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.

Attribute Description
wwid Specifies the WWID of the multipath device to which the multipath attributes apply.
alias Specifies the symbolic name for the multipath device to which the multipath attributes apply.
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 next I/O operation.
failback
Specifies path group failback.
A value of 0 or immediate specifies that as soon as there is a path group whith a higher priority than the current path group the system switches to that path group.
A numeric value greater than zero specifies deferred failback, expressed in seconds.
A value of manual specifies that failback can happen only with operator intervention.
rr_weight
If set to priorities, then instead of sending rr_min_io requests to a path before calling selector to choose the next path, the number of requests to send is determined by rr_min_io times the path's priority, as determined by the prio_callout program. Currently, there are priority callouts only for devices that use the group_by_prio path grouping policy, which means that all the paths in a path group will always have the same priority.
If set to uniform, all path weights are equal.
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 queueing.
A value of fail indicates immediate failure, without queueing.
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 next path in the current path group.

Table 4.2. Multipath Attributes


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 alias.

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_checker          readsector0
              path_selector         "round-robin 0"
              failback              manual
              rr_weight             priorities
              no_path_retry         5
       }
       multipath {
              wwid                  1DEC_____321816758474
              alias                 red
              rr_weight             priorities
        }
}