How does Tape Drive work with DPM when setting up a job?

Hi Guys,

We have migrated from Symantec Backup Exec to System center data protection manager 2012 and I have set up a System Centre 2012 DPM and short term backup on the disk and long term on the tape. I do understand that when DPM backsup  to disk it only copies changes blocks but on the tape drive does it copy the whole backup like if I have 20 VMS on DPM so does it backup 20 whole VMs on the tape drive every night? I am sure there must be a better way to do it.