Comparing Available SCSI Device Access Modes

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	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 cluster-across-boxes	Physical-to-virtual clustering cluster-across-boxes
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.