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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 Setting up DM Multipath. The multipathd daemon must be running in order 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

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.

If you need to use the features "1 queue_if_no_path" option and you experience the issue noted here, you can disable the queueing policy at runtime for a particular LUN, for which all the paths are unavailable.

Procedure

  • Disable queueing for a specific device:

    # multipathd disablequeueing map device
  • Disable queueing for all devices:

    # multipathd disablequeueing maps

After you have disabled queueing for a device, it will remain disabled until multipathd is restarted or reloaded, or until you execute one of the following commands:

  • Reset queueing to the previous value for a specific device:

    # multipathd restorequeueing map device
  • Reset queueing to the previous value for 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 defaults, before exiting the console:

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

    # 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 multipathd interactive command directly from the command line, without starting the interactive console. For example, to check that multipath has picked up any changes to the multipath.conf file, run:

    # multipathd reconfigure