Hello Al
               ADSM will not stack db backups on the same tape. You can do what
you wanted by
adding an admin schedule that does a delete volhistory command for the volume
you wanted to use.
The problem is that del volhist does not take a vol name only a todate and a
type. I would suggest deciding
how many db backups you want to keep and how frequently you want to take them.
Then define a sched that
does the backup and a second sched to expire the unwanted backups (via del
volhist todate=  type=dbb). If you
always do full backups  then this is simply the number of days you wish to be
able to go back. If you are doing
periodic full backups and incrementals in between.  You will want at least the
full backup followed by the incremental
and then the newest full so you can recover to any point in between. With this
method you would want to expire a logical
set at a time. These should allow a full uninterrupted day on the links.

 Regards
             Daniel Curtis ADSM level 1 support