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Chapter 9. Troubleshooting DM Multipath
If you have trouble implementing a multipath configuration, there are a variety of issues you can check for. The following issues may result in a slow or non-functioning multipath configuration:
- The multipath daemon is not running
-
If you find you have trouble implementing a multipath configuration, ensure that the
multipathddaemon is running, as described in Configuring DM Multipath. Themultipathddaemon must be running to use multipathed devices. - Issues with
queue_if_no_pathfeature -
If a multipath device is configured with the
features "1 queue_if_no_path"option, then any process that issues I/O hangs until one or more paths are restored.
9.1. Troubleshooting issues with queue_if_no_path feature
If a multipath device is configured with the features "1 queue_if_no_path" option, then any process that issues I/O hangs until one or more paths are restored. To avoid this, set the no_path_retry N parameter in the /etc/multipath.conf file, where N is the number of times the system should retry a path.
To use the features "1 queue_if_no_path" option without the described problem, you can disable the queueing policy at runtime for a particular LUN, for which all paths are unavailable.
Procedure
Disable queueing:
For a specific device:
# multipathd disablequeueing map deviceFor all devices:
# multipathd disablequeueing mapsAfter you disable queueing, it will remain disabled until you restart or reload
multipathd.
Reset queueing to a previous value:
For a specific device:
# multipathd restorequeueing map deviceFor all devices:
# multipathd restorequeueing maps
9.2. Troubleshooting with the multipathd interactive console
The multipathd -k command is an interactive interface to the multipathd daemon. Entering this command brings up an interactive multipath console. After executing this command, you can enter help to get a list of available commands and Ctrl+D to quit.
Use the multipathd interactive console to troubleshoot problems you might have with your system.
Procedure
Display the multipath configuration, including the default values, before exiting the console:
# multipathd -k multipathd> show config multipathd> Ctrl+D
Ensure that multipath picked up all changes to the
multipath.conffile:# multipathd -k multipathd> reconfigure multipathd> Ctrl+D
Ensure that the path checker is working properly:
# multipathd -k multipathd> show paths multipathd> Ctrl+D
You can also run a single
multipathdinteractive command directly from the command line, without starting the interactive console. For example, to check that multipath picks up all changes to themultipath.conffile, run the following command:# multipathd reconfigure
