In VMware virtual machine how to know RDM mapped drive connected to which LUN in Storage .
1- Go to virtual machine and edit virtual machine setting.
2- Click on Hard disk which is RDM drive.
3- click on Manage Paths
on popup window you will get LUN information 
Note down the LUN information naa.xxxxx…………………..
4- Go to ESX Host >Configuration >Storage Adapters>
5- Click on HBA
6- Go to details 
Check your LUN id and Host LUN ID
Now you can identify your RDM mapped drive on your ESX Host .
Important Note :-The same RDM Mapped drive Host LUN ID may be different on another ESX Host Because ESX Host LUN ID defined by Storage Manager Software while mapping LUN to ESX Host. Best Practice is always give same Host LUN ID for all ESX Hosts while mapping the LUN to ESX Host.