Dell PowerVault MD3200 Owner's Manual - Page 175

Troubleshooting

Page 175 highlights

Troubleshooting Question Answer How can I check if multipathd Run the following command is running? /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. Run rescan_dm_devs instead of rescanThen I map a few LUNs. After scsi-bus for LUN 0 reconfiguration. running rescan-scsibus.sh, LUN 0 does not show up. 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 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. Configuration: Device Mapper Multipath for Linux 175

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Configuration: Device Mapper Multipath for Linux
175
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.