Chapter 6. Troubleshooting DM Multipath

If you have trouble implementing a multipath configuration, there are a variety of issues you can check for.

6.1. DM Multipath troubleshooting checklist

The following issues may result in a slow or non-functioning multipath configuration.

6.1.1. The multipath daemon is not running

If you find you have trouble implementing a multipath configuration, you should ensure that the multipath daemon is running, as described in Chapter 3, Setting up DM Multipath.

The multipathd daemon must be running in order to use multipathed devices.

6.1.2. Issues with queue_if_no_path feature

If a multipath device is configured with features "1 queue_if_no_path", then any process that issues I/O will hang 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 queueing policy at runtime for a particular LUN (that is, for which all the paths are unavailable). The following command disables queueing for a specific device.

multipathd disablequeueing map device

The following command disables 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 one of the following commands.

The following command resets queueing to its previous value for a specific device.

multipathd restorequeueing map device

The following command resets queueing to its previous value for all devices.

multipathd restorequeueing maps

6.2. 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, you can enter a interactive command, or you can enter CTRL-D to quit.

The multipathd interactive console can be used to troubleshoot problems you may be having with your system. For example, the following command sequence displays the multipath configuration, including the defaults, before exiting the console.

# multipathd -k
> > show config
> > CTRL-D

The following command sequence ensures that multipath has picked up any changes to the multipath.conf,

# multipathd -k
> > reconfigure
> > CTRL-D

Use the following command sequence to ensure that the path checker is working properly.

# multipathd -k
> > show paths
> > CTRL-D