Dell EMC PowerVault MD 34XX/38XX Series Storage Arrays Administrator's Guide

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Troubleshooting

Table 1. TroubleshootingThe following table provides answers to frequently asked questions.
Question	Answer
How can I check if multipathd is running?	Run the following command: /etc/init.d/multipathd status
Why does the multipath –ll command output not show any devices?	First verify if the devices are discovered or not. The command #cat /proc/scsi/scsi displays all the devices that are already discovered. Then verify the multipath.conf to ensure that it is been updated with proper settings. After this, run multipath. Then run multipath –ll, the new devices must show up.
Why is a newly mapped LUN not assigned a multipathing device node?	Run rescan_dm_devs in any directory. This should bring up the devices.
I removed a LUN. But the multipathing mapping is still available.	The multipathing device is still available after you remove the LUNs. Run multipath –f <device node for the deleted LUN> to remove the multipathing mapping. For example, if a device related with /dev/dm-1 is deleted, you must run multipath –f /dev/dm-1 to remove /dev/dm-1 from DM mapping table. If multipathing daemon is stopped/restarted, run multipath –F to flush out all stale mappings.
Failback does not happen as expected with the array.	Sometimes the low-level driver cannot autodetect devices coming back with the array. Run rescan_dm_devs to rescan host server SCSI bus and reaggregate devices at multipathing layer.