Virtual to Virtual conversion

I have a VM that has an 800Gb disk that needs to be reduced
in size to accommodate the data that is actually on the disk about 150Gb. A V2V
conversion seems to be the best solution create a clone then V2V on the clone
as the VM is in constant use. What I need to do is apply any changes made to
the original whilst the conversion is underway. Is there a way to snap shot the
original then apply the snapshot to the clone?