The sites/apps will be writing (as well as reading) ALL the time... One of them is a (proprietary) web crawler that will crawl and archive certain types of web resources. (Mainly RSS/XML feeds). Then, another one will crawl/archive URLs, take a screen shot of the URLs too and store them as gif/jpeg/png files.
What sort of static website would need that much storage?
Something like a self-hosted pyvideo.org would probably take a few TBs.
Even that has a search option. I suppose you might want to host a large number of big downloads.