I read your article again and I think I understand it now a bit better.
But for me it's still very strange because with BE 2010 it was the following scenario:
16 tapes: 1x cleaning tape, 2x tapes for archive, 13x tapes where data is stored for 8 weeks.
There were about 9 tapes allways used for storing data for 8 weeks and the other 4 tapes BE didn't use / need because it could store all data from 8 weeks onto the 9 tapes. I also needed just one tape for archive.
Now with BE 2012 the scenario is the following:
16 tapes: 1x cleaning tape, 15x tapes wehre data is stored for 4 (four!) weeks.
BE 2012 still can't store about the same data on 15 tapes for only 4 weeks!
It also needs now 2 tapes for archive.
The type of data stored have not changed, just about 30 to 50gb of data were added over the time.
Our archive created in april have a used capacity of 573GB on the tape with an compression of 1,22 (displayed in BE 2012). Backup Sets shows it stored 758GB and somehow it backed up the fileserver twice.
Our archive created in october have a used capacity of 780GB on the first tape and 26.2 on the second tape.
Backup Sets view in BE tells it stored totally about 461GB.
I discovered now an archive from end of july with the tape drive which is currently in use.
That archive was created with BE 2010, used capacity says 593GB BUT backup sets view says the size was only 446.87GB! So at the moment it looks just like a fault of the tape drive!
I'll gonna replace the tape drive and report back when the new drive is in use.
PS: with archive I mean a tape where the data is stored for lifetime and the backups are full backups.
I have some good news to report.
Today we recived the new Quantum SuperLoader3 replacement unit and now I have run a backup job which saved our IT_Service folder. The folder contains about 8GB data, often .jpg .png .txt .doc(x) .ppt(x) .xls(x) and some .rar and .zip files.
With the old drive the used capacity after the backup was about 12GB data.
Now with the new drive the used capacity is 5.42GB data and it displays a compression ratio of 1,5!!!
So I'll be shure the other backup jobs will also compress the data.
So you see, it's not allways due to the type of data.
However, without asking here I would still searching the problem in Backup Exec.