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.