DVD9 in not 8.5gb
Using BurnAware, size on disc is 8.133mb, 19mb free.
Thus, max size is 8.15gb not 8.5gb, neither 8gb.
This is false advertising, besides DVD9s costing 4x as DVD5 (which is in fact 4.38 not 4.7gb).
DVD5 4.38gb(actual data storage) x 2 = 8.76gb, a loss of 760mb.
DVD9 is not double of DVD5.