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Configuration: Device Mapper Multipath for Linux 219
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
been updated with proper settings.
After this, run multipath. Then run multipath
–ll, the new devices should be displayed.
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 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 219 Wednesday, June 8, 2011 5:01 PM