Basically an RDM (Raw Device Mapping) is a way of presenting Storage LUNs directly to the VMs without being formated as datastores by the ESXi. The LUN is presented to the ESXi using a block-storage protocol and instead of adding Hard Disk to the VM you add RDM which is the LUN without format.
The way of adding it to the VM is quite easy and you can see that here: Add an RDM Disk to a Virtual Machine
I do not recommend configure SR-IOV in case completely needed as you will attach the VM to only one host and you will not enjoy features such as vMotion, HA, etc which makes the ESXi a single point of failure.