Dell MD3200, MD3220 owner manual Troubleshooting, 188, Question Answer

Troubleshooting

Question	Answer
How can I check if multipathd	Run the following command
is running?	/etc/init.d/multipathd status
Why does the multipath	First verify if the devices are discovered or not. The
–llcommand output not	command #cat /proc/scsi/scsi displays all
show any devices?	the devices that are already discovered.
	Then verify the multipath.conf to ensure that it is
	updated with proper settings.
	After this, run multipath. Then run multipath
	–ll, the new devices must be displayed.
Why is a newly-mapped LUN	Run “rescan_dm_devs” in any directory. This must
not assigned a multipathing	bring up the devices.
device node?

I have no LUNs mapped before. Then I map a few LUNs. After running rescan-scsi- bus.sh, LUN 0 does not show up.

I removed a LUN, but the multipathing mapping is still present.

Run rescan_dm_devs instead of rescan- scsi-bus for LUN 0 reconfiguration.

The multipathing device is still there after you remove the LUNs. Run multipath –f<device node for the deleted LUN> to remove the multipathing mapping. For example, if device devices related with /dev/dm-1 is deleted, you must run multipath –f /dev/dm-1to remove /dev/dm-1 from DM mapping table. If multipathing daemon is stopped/restarted, run multipath –Fto flush out all stale mappings.

Failback does not happen as expected with the array.

Sometimes the low level driver cannot auto-detect devices coming back with the array. Run rescan_dm_devs to do a rescan of the host server SCSI bus and re-aggregate devices at multipathing layer.

188

Configuration: Device Mapper Multipath for Linux