I would suggest a Buffalo Link station Duo – Mine is a 6TB total capacity but you can get smaller ones. You could set this up on your Broadband router or other device or to a single PC via USB.
The reason I like it is that I was able to configure it to RAID 1 – this means that the two 3TB disks mirror each other so if there is hardware failure in one disk I have the photos on the other disk.
Effective space is 3TB which seems to be space for about 300,000 photos – plenty for me !