I thought April 1st was 2 days ago already
I don’t want to sound rude or inpolite, and I have no idea what you’re up to, but if you can’t answer this question yourself, you won’t be able to setup a configuration like this yourself. It would involve setting up a clustered environment of dedicated servers, where your Rails app would actually be hosted on one box, leaving the data serving up to a balancer, serving your files transparently from vast number of servers, which in total could serve terabytes of data.
You’ve probably heard of the generous diskspace/bandwidth offerings from Dreamhost (http://www.dreamhost.com/) and I don’t know how good they are in terms of hosting Rails apps. I have always found shared hosts to be good enough for small, low traffic apps, but not ready for high traffic/processor intensive/versatile Rails apps. At one point, you’ll need to have root access (or sudo rights) to tweak your setup.
Shared hosting also has the (in my view biggest) disadvantage of you being dependent on both the hosting support for any server problem/upgrade (and they never fix it as fast as you yourself could on a dedicated box and do upgrades even if you didn’t ask for them, and in my case, mostly during Belgian business hours) and other users on the same box (one of them hits digg or is subject to a vulnerability attack and your site dies with it).
But if you want to host huge files and serve them through a web application, I think there are environments better suited for this than Rails. You are trying to use Rails for the things it’s not really good at and the stuff it excels at are hardly used.
Peter De Berdt