Dell POWERVAULT MD3620I Owner's Manual page 206

Question
I removed a LUN. But the
multipathing mapping is still
available.
Failback does not happen as
expected with the array.
206
Configuration: Device Mapper Multipath for Linux
Answer
The multipathing device is still available after you
remove the LUNs. Run multipath –f
<device node for the deleted LUN>
to remove the multipathing mapping. For
example, if a device 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
flush out all stale mappings.
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.
multipath –F
to