I still don't understand what you're trying to do. It would help if you were to specify a purpose or give more info. What are you trying to compress ? you said several dvd ? if so, they will NOT compress very well at all. Now you're saying you want to compress the files on that HDD, not the HDD image itself, right (I'm trying to assume sanity here).
How small is each file. If they are small files put a batch to make up each rar, that way you don't need dependencies. Oh, and don't use rar, use 7zip.