Tape vs disk cost

[Edward Ned Harvey]

> The current best I have found for large amounts of data is tape (in
> some reasonably current form),
> or 'archival DVD's.  

What's an archival DVD?  Is that a special product?  Whenever I burn and
test DVD's, I would estimate the best-case half-life of a DVD is about 6-12
months.  That is ... If I burn a bunch of DVD's, then approx 6 months later,
half of them are bad.