Best Server Storage Setup?

new-black-hand asks: "We are in the process of setting up a very large storage array and we are working toward having the most cost-effective setup. Until now, we have tried a variety of different architectures, using 1U servers or 6U servers packed with drives. Our main aims are to get the best price per GB of storage that we can, while having a reliable and scalable setup at the same time. The storage array will eventually become very large (in the PB range) so saving just a few dollars on each server means a lot. What do people out there find is the most effective hardware setup? Which drives and of what size? Which motherboards, etc? I am familiar with the Petabox solution which is what the Internet Archive uses — they have made good use of Open Source software. So what are some of the architectures out there that, together with Open Source, can give us a storage array that is much better than the $3 per GB plus that the commercial vendors ask for?"