[drauk]

We do this sort of stuff pretty routinely. Works fine.

I wouldn't rsync the files between the machines. DRBD won't help you either; you can only read from one of the two mirrored pair with DRBD (i.e. you could send the file from disk A to disk B, but you can't read from Disk B whilst it's connected to Disk A).

The NFS solution will work perfectly well. Start with it on your MySQL server and if you need more performance later you can scale it up by using a dedicated NFS server. You can use RSync to back it up though. Or if you want to spend the money and get even more resilience, use DRBD to do real-time backups of your database and NFS server.

Why do you want/need to use Round Robin if you've got hardware load balancers?

More generally, don't even think about using Apache. Lighttpd and XCache will give you a lot more capacity.