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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 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.

9.1. Troubleshooting issues with queue_if_no_path feature
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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

  1. Disable queueing:

    • For a specific device: 

      # multipathd disablequeueing map device
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    • For all devices: 

      # multipathd disablequeueing maps
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      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
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    • For all devices: 

      # multipathd restorequeueing maps
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9.2. Troubleshooting with the multipathd interactive console
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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

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

    # multipathd -k
multipathd> show config
multipathd> Ctrl+D
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  2. Ensure that multipath picked up all changes to the multipath.conf file: 

    # multipathd -k
multipathd> reconfigure
multipathd> Ctrl+D
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  3. Ensure that the path checker is working properly: 

    # multipathd -k
multipathd> show paths
multipathd> Ctrl+D
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  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
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