C1556D not compressing data using win2k ntbackup

[BR734547]

We are using a C1556D external 24gb dat drive to run backups.

the problem is that at this point, our data surpasses 12gb and ntbackup asks me to insert a free tape. in the job properties I can see that the "Use Hardware Compresion" option is enabled. But nevertheless it won't compress. Im using HP DDS3 Dat tapes 12/24GB.

What can be wrong?

[Eugeny Brychkov]

You're backing up already compressed files. Native drive's capacity is 12GB, and you can achieve 24GB with compression ratio 2:1.
Check drive with HP LTT http://www.hp.com/cposupport/information_storage/support_doc/lpg50128.html , run compression test
Eugeny