The buffalo linkstation quad is what you want if you want media sharing capability as well:
ht.com.au | Buffalo LinkStation Quad - NAS - 4 TB - Serial ATA-150 - HD 1 TB x 4 - RAID 0, 1, 5, 10, JBOD - Gigabit Ethernet
not only is it cheaper, it also actas as a torrent downloader if you want it to.
There are cheaper versions if you don't need something with space for 4 drives.