Many thanks,
I was thinking to cold migrate it going by the link you pasted.
"
If you wish to cold migrate a virtual machine without cloning or converting its
RDMs, remove them from the configuration of the virtual machine before
migrating. You can delete the RDM from the disk when removing it (the raw LUN
contents are not changed). Re-add them to the configuration when completed"
I think the above is true for anything below ESX5.x ......
I think with ESX 5 I can migrate it online through the advanced option.
Let me know if I am getting it right?
-Rahul