Another option that backs up Centera in its native format VBR (View, Backup, Recover) from DataTrust Solutions. Unlike the Altus option which stores data in a proprietary format on tape only, VBR writes to disk (local or networkded) and does not stor...
Datatrust solutions has a product specifically to migrate files managed by diskxtender.
The software is called onepass for dx and it should do what you need.
http://www.datatrustsolutions.com