Originally from servervault by a user named Johan
Bonus: a better way to copy
If you have thinly provisioned client, you can use the command-line tool vmkfstools like so:
vmkfstools -i /vmfs/volumes/path_to_datastore/path_to_source_vm/vmname.vmdk /vmfs/volumes/path_to_dest_datastore/path_to_dest_vm/vmname.vmdk -d thin &
This will clone (-i) the vmdk file and make sure the destination file is thinly (-d thin) provisioned. The & at the end of the command will make sure you get your command prompt back.
It will copy much faster than the GUI copy does, and you can cancel it easier.
canceling a vmkfstools copy
ps |grep vmkfstools Note down the PID. kill 12345
Where 12345 is the first number listed on the vmkfstools line.