another points of interest:

. required restore performance. The restore 
is The purpose of any backup. 
This will most likely
have imlications on number of tape drives in the library
and the type of tape HW to choose, as well as
on network, cpu, disk subsystem palnning.

. necessary labor time. While masssivly automated,
adsm (as well as another automated systems) still
require supervising.

. number of files, number of MBytes changed daily,
total No. of MBytes to be backed up, number of different
file versions to be kept, for how long, ..

. required grade of fault-tollernace.
Is it OK to have each file on 2 media (only)
e.g. one off-site and one on-line?

bye
Juraj Salak