Might use Cascade drive, here is the explanation of this:
You can cascade (link) multiple stand-alone tape drives together to create one
logical drive. By cascading the tape drives, backup jobs can automatically "roll"
to the "media" in the next tape drive when the media is filled. Although multiple
tape drives are linked to form the cascaded drive pool, only the name of the
cascaded drive pool is listed as the destination device when a backup job is created.