Jon ...

In a recent Computerworld white paper, entitled "The Economics of a Storage
Strategy"
http://www.computerworld.com/cwi/wp/story/0,,NAV63-130_STO65180,00.html
Randy Kerns writes that the #1 issue with storage is the cost of
administration!

IMHO, don't concern yourself about "cost of tape cartridges to hold 7 years
worth of data".
Concentrate instead on a business strategy to ensure reliable storage and
retrieval.
If the storage requirement is realistically 7 years, then the enterprise has
already
established the importance of the data!

The question should really be "what storage strategy is optimal for my
environment?"