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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.
Note
When a multipath device is being created or modified, the path group status and the dm status are not known. Also, the features are not always correct. When a multipath device is being listed, the path group priority is not known.
