I second this. I just bought my 2nd DNS 323 after the first one got full. (its cheaper to buy 2 DNS 323 which are 2 bays, compared to getting the 4 bay version). I shoot a lot of pics, and at 20-25 meg per RAW file, it adds up quickly.
The first is stacked with 2x1.5 TB drives, the 2nd with 2x2TB drives. I've got them running in RAID 1 for hardware redundancy. Great little devices and cheap (150$ Canadian). With the latest firmware you can even run NFS, and a native bittorrent client.