Backup Exec 2010 R3 is not using tapes to full capacity

Dear Technical Team,

I have been using Backup Exec 2010 R3 for quite sometime, but last week backup ends with only using the tapes to half capacity only i.e., 379GB used out of 800GB original space. Tapes are C7973A 800GB RW LTO3. Backup exec was going smoothly until last week.

I have not done any changes in Backup Exec options or Media properties. Now all the tapes got full and drives are waiting for empty tapes which i cannot put bcoz both the drives are busy and i cannot execute unlock command to put scratch tapes. So I have cancelled one of the job and put new tapes erase it.

But anybody can tell why the capacity of tapes was not utilized fully instead only half. Is there any compression option i need to use.

Pls. help me out.

Thanks