Hi,
If the device is supporting hardware compression, it can be enabled in
Backup Exec.
It may not be possible to achieve twice the amount of native capacity.
Refer: http://seer.support.veritas.com/docs/199542.htm
You may try backup using Windows native backup utility. Stop all the Backup
Exec services from services applet and run NTbackup. Verify the tape
capacity and compression.
Additionally upgrade the firmware and install latest drivers.
NOTE : If we do not receive your reply within two business days, this post would be marked "assumed answered" and would be moved to "answered questions" pool.