228 Configuration: Device Mapper Multipath for LinuxTroubleshootingQuestion AnswerHow can I check if multipathdis running?Run the following command/etc/init.d/multipathd statusWhy does the multipath–ll command output notshow any devices?First verify if the devices are discovered or not. Thecommand #cat /proc/scsi/scsi displays allthe devices that are already discovered.Then verify the multipath.conf to ensure that it isupdated with proper settings.After this, run multipath. Then run multipath–ll, the new devices must be displayed.Why is a newly-mapped LUNnot assigned a multipathingdevice node?Run “rescan_dm_devs” in any directory. This mustbring up the devices.I have no LUNs mapped before.Then I map a few LUNs. Afterrunning rescan-scsi-bus.sh, LUN 0 does notshow up.Run rescan_dm_devs instead of rescan-scsi-bus for LUN 0 reconfiguration.I removed a LUN, but themultipathing mapping isstill present.The multipathing device is still there after youremove the LUNs. Run multipath –f node for the deleted LUN> to remove themultipathing mapping. For example, if devicedevices related with /dev/dm-1 is deleted, you mustrun multipath –f /dev/dm-1 to remove/dev/dm-1 from DM mapping table. If multipathingdaemon is stopped/restarted, run multipath –Fto flush out all stale mappings.Failback does not happen asexpected with the array.Sometimes the low level driver cannot auto-detectdevices coming back with the array. Runrescan_dm_devs to do a rescan of the host serverSCSI bus and re-aggregate devices atmultipathing layer.
