Mapping RAW Disks (RDM) in ESXi 4.0, 4.1, 5.0, 5.1
When you need have raw drive to a VM in ESXi without passing the whole controller to the VM, you’ll need RDM (Raw Device Mapping).
Here is the jist, in a SSH session with ESXi server:
vmkfstools -z /vmfs/devices/disks/
More details
http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1017530