If you're talking about building some sort of archival-type repository (like, keeping years worth of satellite imagery, for example), then you should probably look at the Centera from EMC. They scale into the petabyte range.
Providing you can find some sort of filesystem to support it (good luck), you could stash multiple arrays behind your host, or you could put in a TagmaStore from HDS with several arrays behind it. I'm not entirely sure how large the Tagma will scale, but the number 32 petabytes sticks in my head from a whitepaper somewhere.
I'd also question the perceived need to create one big filesystem to hold your whole petabyte of data. I'm a storage geek for a living, and I've found that usually after you start drilling into the application requirements, you find out that the app folks are either trying to use a data warehouse solution that's too small for the environment, or they're simply not aware of other alternatives available in their chosen app. No offense, but it sounds like you've had snowshoes strapped to your feet and directed to take a stroll through a minefield.
