The ways of accessing a SCSI-based storage device include a virtual disk file on a VMFS datastore, virtual mode RDM, and physical mode RDM.

The following table provides a comparison of features available with the different modes.

Table 1. Features Available with Virtual Disks and Raw Device Mappings
ESXi Features Virtual Disk File Virtual Mode RDM Physical Mode RDM
SCSI Commands Passed Through No No


REPORT LUNs is not passed through

vCenter Server Support Yes Yes Yes
Snapshots Yes Yes No
Distributed Locking Yes Yes Yes
Clustering Cluster-in-a-box only Cluster-in-a-box


Physical-to-virtual clustering


SCSI Target-Based Software No No Yes

Use virtual disk files for the cluster-in-a-box type of clustering. If you plan to reconfigure your cluster-in-a-box clusters as cluster-across-boxes clusters, use virtual mode RDMs for the cluster-in-a-box clusters.