You can restrict the job to a specific slot in a library by using Partitioning and then have a human admin make sure the correct tape is in the slot at the required times, but there is no way to force BE to always use a tape based on it's label - the following is what I posted recently in another thread about tape selection choices during overwrites (appends always go to an appendable tape in the media set and if more than one tape meets this requirement I think they use the earliest last written to timings to select):
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Other than targetting partitions there is no simple (i.e. easy to avoid human error) way to fix BE to use a specific tape (cartridge) - there is a chapter in the admin guide that covers how an overwritable tape is chosen (when one is needed) as you can adjust the selection order based on settings.
At the end of the day Backup Exec is designed to try and find a suitable tape to write to, whenever one is needed, this is because to most customers running (and completing) the current backup is more critical than exactly what tape it ends up being written to. In the scenario where you expect your backup to complete but have a disaster while the backup job is asking for a tape, you could lose a day's worth of data just because you stopped Backup Exec from using any suitable, available tape.
