Switching a RDM from physical to virtual compatibility mode

To change a RDM from physical to virtual compatibility mode:

Note: VMware recommends that you backup your configuration before performing these steps.

1. Power off the virtual machine.
2. Right-click the virtual machine and click Edit Settings.
3. Note the SCSI device that the RDM is using (for example, SCSI0:5).
4. Remove the RDM hard disk from the virtual machine, ensure that the Delete from Disk option is selected, and then click OK.
   
   Note: Unlike VMDK files, the Delete from Disk option removes only the RDM pointer files. Data on the RDM remains intact.
   
   
5. Right-click the virtual machine and click Edit Settings.
6. Add the RDM back to the virtual machine as a new disk and select virtual compatibility mode. Ensure to use the SCSI device that you noted in Step 3.
7. Power on the virtual machine.

What is the difference between Physical Compatibility Mode and Virtual Compatibility Mode :

The default is physical compatibility mode. This allows the Guest OS to access the hardware directly, and this can be useful for:

• Situations where SAN snapshot capabilities require this

• Physical-to-virtual clustering (required)

Virtual compatibility allows the VM to use VMware snapshots and other advanced functionality while still providing direct LUN access. This is also called a Raw Device Mapping (RDM). The virtual disk file is essentially a symbolic link to the mapped LUN. This is the preferred mode to use if possible since you get the benefits of VM snapshots.