I’ve seen some docs and data out there that exhibit confusion over the file extension for an RDM file, describing it as .rdm.vmdk or -rdm.vmdk or other variations. A quick ls from a VM with a RDM shows:
there is a normal descriptor file with a .vmdk extension and the actual mapping file with a -rdmp.vmdk nomenclature.
du shows the mapping file as being empty (which it is being a brand new RDM map)
The VMDK descriptor however contains pretty much what you’d expect – the who what where of the virtual drive:
More interesting is the datastore browser is RDM aware and (unlike for regular VMDKs) shows the mapping file and descriptor as separate files.