What about FreeNAS and Openfiler? It's awesome and cost you $0.00
Here is the 40TB server that I built for my client.
Running over 2yrs, use all WD green drives
Data protected (RAID50)
Green - only consume 180W
FTP, HTTP, RSYNC, NFS, ATP, SMB, iTUNE Server, Bittorrent...
Immune to ad-ware and...