>I am looking at what to do in the next year or so when our tape library >becomes full. ...
Assuming that you don't have room for another frame, your management could consider upgrading to higher-density drives and effectively increase the capacity of your library. Too costly? They need to consider the cost of coming up with an externals scheme, the cost of misplaced external tapes, the cost of missed mount requests, etc. all of which impacts the business's bottom line. Richard Sims, BU