Troubleshooting - Dell PowerVault MD3220 Owner's Manual

Troubleshooting

Question
How can I check if multipathd
is running?
Why does the multipath
–ll command output not
show any devices?
Why is a newly-mapped LUN
not assigned a multipathing
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.
Failback does not happen as
expected with the array.
Answer
Run the following command
/etc/init.d/multipathd status
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 should be displayed.
Run "rescan_dm_devs" in any directory. This should
bring up the devices.
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-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.
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.
Configuration: Device Mapper Multipath for Linux
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