Can I perform a VMware backup of RDM virtual disks?
To perform VMware backup of raw device mapped (RDM) virtual disks
Unitrends’ Virtualization Protector supports VMware backup of virtual RDM disks. It does not, however, support backup of virtual machines configured with physical RDM. For these VMs, you must use agent-based backup.
For details, see the following section of the Unitrends Administrator’s Guide: About VMware backups.