Exchange Offline defrag

The current volume on our SAN containing the Exchange 2003 IS has 2Gb left.
Private store is at 45Gb and Public store is at 82Gb (enterprise version).
Due to the space requirements for a defrag, we will dismount and move the Private store to a larger volume before running the offline defrag.
Apart from a full backup? any other suggestions to help this defrag run smooth and fast(est).
Regards, Ivan.