RDM lets you give a permanent name to a device by referring to the name of the mapping file in the /vmfs subtree.

The example in Example of Name Resolution shows three LUNs. LUN 1 is accessed by its device name, which is relative to the first visible LUN. LUN 2 is a mapped device, managed by an RDM on LUN 3. The RDM is accessed by its path name in the /vmfs subtree, which is fixed.

Example of Name Resolution
The graphic shows three LUNs. LUN 1 is accessed by its device name, which is relative to the first visible LUN. LUN 2 is a mapped device, managed by an RDM on LUN 3. The RDM is accessed by its path name in the /vmfs subtree, which is fixed.

VMFS uniquely identifies all mapped LUNs, and the identification is stored in its internal data structures. Any change in the SCSI path, such as a Fibre Channel switch failure or the addition of a new host bus adapter, can change the device name. Dynamic name resolution compensates for these changes by adjusting the data structures to retarget LUNs to their new device names.