To export a VMDK virtual disk to media-independent format:
vmkfstools -e /path/to/temp/Tempfile.vmdk /vmfs/volumes/datastore1/Hostname/Hostname.vmdk
The exported file will consist of a tiny descriptor file plus a set of sparse files up to 2 Gbytes each.
To import the VMDK back into VMFS so it can be used by a virtual machine:
vmkfstools -i /path/to/temp/Tempfile.vmdk /vmfs/volumes/datastore1/Hostname/Hostname.vmdk
The descriptor file will be used to combine the sparse files back into the original monolithic VMDK file.