Summary
NDMP backup jobs consume more tapes than the size of the backup data would require.
Symptoms
NDMP backup jobs may consist of multiple sub-tasks. In this case, each task consumes a complete tape regardless of its remaining capacity.
Resolution
Disable the "Mark Original Offsite" option in the Set Job Destination Options screen. With the option enabled, the tape is marked offsite and dismounted at the end of each sub-task. A new tape is mounted for the next task. Disable this option to prevent over usage of backup tapes.