I don’t like this question since you can also use clustering across ESXi hosts when using Virtual Mode RDM’s. But since VMWare recomends using physical mode i think D is indeed what they want to hear.

Although Hardware Acceleration could also be true since with Physical Mode Raw Device Mapping you directly connect to the underlying storage and thus can leverage whatever features the storage provider has.

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VSAN

You need to use raw LUNs with RDMs in the following situations:

When SAN snapshot or other layered applications run in the virtual machine. The RDM better enables scalable backup offloading systems by using features inherent to the SAN.

In any MSCS clustering scenario that spans physical hosts — virtual-to-virtual clusters as well as physical-to-virtual clusters. In this case, cluster data and quorum disks should be configured as RDMs rather than as virtual disks on a shared VMFS.

Think of an RDM as a symbolic link from a VMFS volume to a raw LUN. The mapping makes LUNs appear as files in a VMFS volume. The RDM, not the raw LUN, is referenced in the virtual machine configuration. The RDM contains a reference to the raw LUN.

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