Compression Ratio different

Good morning,

We have problems against compression ratio with our backup exec 12.5.

There is one tape with compression ratio 1.9.1 and that is all right.

Rest of tapes is 1:4:

Compression type Hardware (if available, otherwise software)

Device: HP Ultrium 2-SCSI (compression enabled Block and buffer size 64 KB Write Single block mode and Write SCSI PassTrough mode enabled.)

Backup runs on newest update of BE 12.5

I hope anyone can help us.