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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
getuid_callout Specifies the default program and arguments to call out to obtain a
unique path identifier. An absolute path is required.
prio_callout Specifies the default program and arguments to call out to obtain a
path weight. Weights are summed for each path group to determine
the next path group to use in case of failure. "none" is a valid value.
path_checker Specifies the default method used to determine the state of the
paths. Possible values include readsector0 and tur,
emc_clariion, hp_sw, and directio.
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 with 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 m anual specifies that failback can happen only with
operator intervention.
features The extra features of multipath devices. The only existing feature is
queue_if_no_path, which is the same as setting
no_path_retry to queue.
hardware_handler Specifies a module that will be used to perform hardware specific
actions when switching path groups or handling I/O errors. Possible
values include 0, 1 emc, and 1 rdac. The default value is 0.
rr_min_io (RHEL 4.8 and later) Specifies the number of I/O requests to route
to a path before switching to the next path in the current path
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Chapter 4. The DM-Multipath Configuration File
group. The default value is 1000.
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. The default value is
uniform.
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 queuing.
A value of queue indicates that queuing should not stop until the
path is fixed.
The default value is (null).
flush_on_last_del (RHEL 4.7 and later) If set to yes, the multipathd daemon will
disable queueing when the last path to a device has been deleted.
The default value is no.
The following example shows a device entry in the multipath configuration file.
# }
# device {
# vendor "COMPAQ "
# product "MSA1000 "
# path_grouping_policy multibus
# path_checker tur
# rr_weight priorities
# }
#}
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Red Hat Enterprise Linux 4 DM Multipath
Chapter 5. DM-Multipath Administration and Troubleshooting
This chapter will provide information on administering DM-Multipath on a running system. It includes
sections on the following topics:
Multipath Command Output
Multipath Queries with multipath Command
Multipath Command Options
Multipath Queries with dmsetup Command
Troubleshooting with the multipathd Interactive Console
Resizing an Online Multipathed Device
5.1. Multipath Command Output
When you create, modify, or list a multipath device, you get a printout of the current device setup. The
format is as follows.
For each multipath device:
action_if_any: alias (wwid_if_different_from_alias)
[size][features][hardware_handler]
For each path group:
\_ scheduling_policy [path_group_priority_if_known]
[path_group_status_if_known]
For each path:
\_ host:channel:id:lun devnode major:minor [path_status] [dm_status_if_known]
For example, the output of a multipath command might appear as follows:
mpath1 (3600d0230003228bc000339414edb8101) [size=10
GB][features="0"][hwhandler="0"]
\_ round-robin 0 [prio=1][active]
\_ 2:0:0:6 sdb 8:16 [active][ready]
\_ round-robin 0 [prio=1][enabled]
\_ 3:0:0:6 sdc 8:64 [active][ready]
If the path is up and ready for I/O, the status of the path is ready or active. If the path is down, the
status is faulty or failed. The path status is updated periodically by the multipathd daemon
based on the polling interval defined in the /etc/multipath.conf file.
The dm status is similar to the path status, but from the kernel's point of view. The dm status has two
states: failed, which is analogous to faulty, and active which covers all other path states.
Occasionally, the path state and the dm state of a device will temporarily not agree.
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Chapter 5. DM-Multipath Administration and Troubleshooting
Note
When a multipath device is being created or modified, the path group status and the dm status
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