As per your description, you are using physical RDMs (2 pcs rdm physical mode.)
You do not need to shutdown the server. Please go through the steps as below from the KB VMware Knowledge Base
Physical compatibility mode
Physical compatibility mode RDMs, which are also known as passthru RDMs, expose the physical properties of the mapped LUN to the guest operating system. For the guest operating system to recognize the added space to the expanded mapped LUN, perform a rescan from the ESX host, then from the guest operating system. This process does not require rebooting the virtual machine or the ESX host.
No changes to the RDM files (.vmdk or metadata pointer) are required to take advantage of the added disk space.