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Chapter 8. Troubleshooting DM Multipath
Troubleshoot multipath configuration issues by checking daemon status, "queue_if_no_path" feature problems, and the multipathd interactive console for diagnostics.
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. - Issues with
queue_if_no_pathfeature - If a multipath device is configured with the "1 queue_if_no_path" option, any process issuing I/O will hang. It remains hung until one or more paths are restored.
8.1. Troubleshooting issues with queue_if_no_path feature
Resolve I/O hangs from queue_if_no_path by setting no_path_retry N in /etc/multipath.conf, limiting retries when all paths fail. You can also disable queueing at runtime for specific Logical Unit Numbers (LUNs) to prevent applications from hanging during path outages.
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
8.2. Troubleshooting with the multipathd interactive console
Use the multipathd -k interactive console to troubleshoot multipath issues in real time. This console provides access to status info, config details, and control commands. Type help for commands and press Ctrl+D to exit without disrupting services.
Procedure
Display the multipath configuration, including the default values, before exiting the console:
# multipathd -kmultipathd> show config multipathd> Ctrl+DEnsure that multipath picked up all changes to the
multipath.conffile:# multipathd -kmultipathd> reconfigure multipathd> Ctrl+DEnsure that the path checker is working properly:
# multipathd -kmultipathd> show paths multipathd> Ctrl+DYou 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
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