The only reason I can think of for using partitions in a tape library is to force BE to write to a particular tape or to a particular set of tapes. This is a desirable outcome for some organizations. However, this comes at a price. When more tapes are needed and there is none in the targeted partition, BE will not be able to get the tapes from another partition even if they are available and the job will fail. Backup job failures are bad for the organization. The reasons why this is so are covered in the second paragraph of my article
If the library is not partitioned, then BE can get a tape from another media set and complete the job.
BE will only take a tape from another media set if there are insufficient tapes in the targeted media set. This could be due to setting the OPP (overwrite protection period) incorrectly so that there is no overwriteable tape available or the data has grown so much that it exceeded the number of tapes allocated to the media set. Having partitions only worsen the situation by preventing BE from taking tapes from other partitions and thus causing the job to fail.
It is my contention that partitions in a tape library should be banned. They are hazardous to your backups. Do you agree or don’t agree? Take the survey to the right of this blog.