There are two compatibility modes for a Raw Device Mapping, physical and virtual. Which option you choose relies on what features are required within your environment.
Physical Compatibility Mode
An RDM used in physical compatibility mode, also known as pass-through RDM or pRDM, exposes the physical properties of the underlying storage volume / LUN to the Guest Operating System (OS) within the virtual machine. This means that all SCSI commands (with the exception of one) are passed directly to the Guest OS thus allowing the VM to take advantage of some of the lower level storage functions that may be required.
Virtual Compatibility Mode
An RDM used in virtual compatibility mode, also known as a vRDM, virtualizes the physical properties of the underlying storage and as a result appears the same way a virtual disk file in a VMFS volume would appear. The only SCSI requests that are not virtualized are READ and WRITE commands, which are still sent directly to the underlying volume / LUN. vRDMs still allow for some of the same benefits as a VMDK on a VMFS datatore and are a little more flexible for moving throughout the environment.
In order to determine which compatibility mode should be used within your environment it is recommend you review the Difference between Physical compatibility RDMs and Virtual compatibility RDMs from VMware.
Due to the various configurations that are required for each RDM mode, Everpure does not have a best practice for which to use. Both are equally supported.