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.

To help you choose among the available access modes for SCSI devices, Features Available with Virtual Disks and Raw Device Mappings provides a quick comparison of features available with the different modes.

Features Available with Virtual Disks and Raw Device Mappings

ESX Features

Virtual Disk File

Virtual Mode RDM

Physical Mode RDM

SCSI Commands Passed Through

No

No

Yes

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 and cluster-across-boxes

Physical to Virtual Clustering

SCSI Target-Based Software

No

No

Yes

VMware recommends that you 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.