The easiest way to convert .vmdk images to use the new disk format is to use vcsadmin after the .vmdk image has been loaded into the library.
There cannot be active deployments, or snapshots attached to any app configs using the image.
The command is:
Usage: imageconvert [options] libraryPath sourceVersion targetVersion
options are:
-image <image> Path and filename of the target image from the specified library's root directory.
valid versions are:
'VMDK3' (Hardware Version 3 2-file VMDK format), 'VMDK4' (Hardware Version 4 2-file VMDK format)
so for example for the file myImage.vmdk that has been saved in the library under Library/Templates/myImage.vmdk and the base library path is \\filehost\library\
'imageconvert -image \Templates\myImage.vmdk \\fileshost\library VMDK3 VMDK4'