I know this is old now, but a while back I came across this blog post by the company Backblaze. They detail how they build these custom “storage pods” that get rack mounted in their datacenter for online storage. In their post, they show how using this method they manage to save tons of money that would have been otherwise spent on Amazon S3 storage, EMC / Dell or Sun solutions. Each storage pod can be looked at as one building block of a much larger storage solution.
I think this design is great and if I had the space / resources I would defintely attempt one of these as a project for myself. To quote their site, the storage pods contain the following hardware:
“one pod contains one Intel Motherboard with four SATA cards plugged into it. The nine SATA cables run from the cards to nine port multiplier backplanes that each have five hard drives plugged directly into them (45 hard drives in total).”
Here is a youtube video showing the design of one storage pod.
Read up more at Backblaze blog