6.5.1

Table Of Contents
Raw Device Mapping with Virtual Machine Clusters
Use an RDM with virtual machine clusters that require access to the same raw LUN for failover scenarios.
The setup is similar to that of a virtual machine cluster that accesses the same virtual disk file, but an
RDM replaces the virtual disk file.
Figure 193. Access from Clustered Virtual Machines
address
resolutiion
Host 4Host 3
VMFS volume
“shared” access
VM4VM3
mapped
device
mapping file
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 191. 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.
vSphere Storage
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