How much of your terabyte is yours? The duplication seems to be at least three times (more?), so that would be 333GB. Note: it doesn't matter how finely you cut it up, you need duplication to avoid loss.

It can be ameliorated by the cloud tricks of compression and git-like copy-detection across nodes (people downloaded the same movie, music, image, document, software etc) giving aggregate savings.

Of course, most people won't use their full quota initially, and meanwhile more adopters come online with fresh excess capacity... a kind of ponzi-scheme/chain-letter (to be fair, as drive prices fall over years, units will likely become 2TB, 4TB etc).