Backblaze has a history of releasing their storage designs, right down to drive models, chipsets and prices.

It costs them about $11k to build 180Tb, $60/Tb, or 6 cents per GB.

They are using the i3-2100 – the same as I am using in my HTPC. The CPU is still pretty powerful, but frugal on power.

I think low power storage is a great replacement for tape backups. With de-duplication, and SAN snapshots, tape backup gets very messy.

I developed a storage server based on an embedded amd 350 , and green drives, it was even lower power – and surprising performance, plenty for backup.

http://blog.backblaze.com/2013/02/20/180tb-of-good-vibrations-storage-pod-3-0/