On physical RDM and virtual RDM

Why don't we use virtual RDM (RAM Device mapping--bare disk mappings)?

Then the physical RDM and virtual RDM are contrasted from the structure, function and capacity, as follows.

Structure comparison:

The virtual mode of the naked device mapping is a fully virtualized device mapping. Its client operating system files are identical to the virtual disk files in the VMFS system, which makes the hardware features truly hidden, allowing the customer to realize the benefits of VMFS when the bare disk is mapped, such as advanced data protection, Simplified process development to render the same properties as the virtual disk.

(Virtual mode for a mapping specifies full virtualization of the mapped device. It appears to theguest operating system exactly the same as a VI rtual disk file in a VMFS volume. The real hardware characteristics are hidden. Virtual mode allows customers using raw disks to realize the benefits of VMFS such as advanced file locking for Data prote Ction and redo logs for streamlining development processes. Virtual mode is also more portable across storage hardware, presenting the same behavior as a virtual disk file.)

The physical mode of naked device mappings refers to device mappings for minimal SCSI virtualization, which maximizes the flexibility of San management software. In physical mode, all SCSI commands for Vmkernel are passed directly to the device, with one exception: the report LUN command is virtualized, which vmkernel the virtual machines that can isolate LUNs. Otherwise, the physical properties of all the underlying hardware are exposed. Physical mode is useful for running a San management agent or other SCSI-based software in a virtual machine. Physical mode also allows for cost-effective high availability of virtual to physical clusters.

(physical mode for a raw device mapping specifies minimal SCSI virtuali zation of the mapped device, allowing Flexibility for SA N management software. In physical mode, the "Vmkernel passes all SCSI commands to" device, with one exception:the, and the LUNs command is Virt Ualized, so this vmkernel can isolate the LUN for the owning virtual machine. Otherwise, all physical characteristics of the underlying hardware are. Physical mode is useful to run SAN management agents or other SCSI target based software in the virtual machine. Physical mode also allows virtual to physical clustering for cost-effective high availability)