Dell PowerVault MD3220 - Manual (Page 188)

188 Configuration: Device Mapper Multipath for Linux
Troubleshooting
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
updated with proper settings.
After this, run multipath. Then run multipath
–ll
, the new devices must be displayed.
Why is a newly-mapped LUN
not assigned a multipathing
device node?
Run “rescan_dm_devs” in any directory. This must
bring up the devices.
I have no LUNs mapped before.
Then I map a few LUNs. After
running rescan-scsi-
bus.sh
, LUN 0 does not show
up.
Run rescan_dm_devs instead of rescan-
scsi-bus
for LUN 0 reconfiguration.
I removed a LUN, but the
multipathing mapping is still
present.
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.
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.
book.book Page 188 Tuesday, June 18, 2013 2:53 PM