186 Configuration: Device Mapper Multipath for Linux
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 show
up.
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 some LUNs. After
running rescan-scsi-bus.sh, LUN 0
doesn’t 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
there.
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 rescan host server SCSI
bus and re-aggregate devices at multipathing
layer.
Question Answer
book.book Page 186 Wednesday, May 26, 2010 2:14 PM