HP LTO-2 Ultrium 400GB Data Cartridge (C7972A) only back ups 280 gb using symantec baCKUP EXEC 10 R3

Hi all,

We have Symantec Backup Exec 2010 R3 to backup our data on a set of HP LTO-2 Ultrium 400GB Data Cartridge (C7972A) tapes, the problem is that the tape only backup 280gb instead of its full capacity 400gb, kindly what I am missing here?

Thanks