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

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