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Chapter 8. Troubleshooting DM Multipath

Troubleshoot multipath configuration issues by checking daemon status, queue_if_no_path feature problems, and using 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 multipathd daemon is running, as described in Configuring DM Multipath. The multipathd daemon must be running to use multipathed devices.
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.

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 LUNs to prevent applications from hanging during path outages.

Procedure

  1. Disable queueing:

    • For a specific device: 

      # multipathd disablequeueing map device
      Copy to Clipboard Toggle word wrap

    • For all devices: 

      # multipathd disablequeueing maps
      Copy to Clipboard Toggle word wrap

      After you disable queueing, it will remain disabled until you restart or reload multipathd.

  2. Reset queueing to a previous value:

    • For a specific device: 

      # multipathd restorequeueing map device
      Copy to Clipboard Toggle word wrap

    • For all devices: 

      # multipathd restorequeueing maps
      Copy to Clipboard Toggle word wrap

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

  1. Display the multipath configuration, including the default values, before exiting the console: 

    # multipathd -k
multipathd> show config
multipathd> Ctrl+D
    Copy to Clipboard Toggle word wrap

  2. Ensure that multipath picked up all changes to the multipath.conf file: 

    # multipathd -k
multipathd> reconfigure
multipathd> Ctrl+D
    Copy to Clipboard Toggle word wrap

  3. Ensure that the path checker is working properly: 

    # multipathd -k
multipathd> show paths
multipathd> Ctrl+D
    Copy to Clipboard Toggle word wrap

  4. You can also run a single multipathd interactive command directly from the command line, without starting the interactive console. For example, to check that multipath picks up all changes to the multipath.conf file, run the following command: 

    # multipathd reconfigure
    Copy to Clipboard Toggle word wrap
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