Shared files for multiple Web Servers Behind a Load Balancer

I am migrating our MU website to multiple web servers behind a Load Balancer.

The Load Balancer is in place and sending traffic to one web server currently running APC / apache.

What is the solution for the file system? Once we have more than one web server, I can't just sync the uploads directory between each server as it is about 40 gigs. Also, quick cache writes its files to a wp-content/cache directory. If that isn't shared, then each web server has to generate their own cached version.

I have tried a persistent storage solution and mounted it to the /home directory, but that was far too slow.

What is the right way to do this? I am sure many people have solved this already.