It's not currently bigger than Buffalo's TeraStation Pro, but with a little fettling the Princeton DN-503AH-PDC NAS certainly could be. Packing five 1TB hard-drives, it has a total capacity of 5TB; that's one down on the 6TB TeraStation Pro, but since that NAS has only four bays to the Princeton's five it has to rely on larger 1.5TB HDDs. Switch the DN-503AH-PDC's discs for 1.5TB versions and you'd have 7.5TB capacity, which is perhaps the largest we've seen on a small-business backup device.
As standard, though, 5TB is still plenty capacious. Various RAID setups are possible, including 0, 1, 5 and 6, and the drives are kept in easily-accessed caddies for speedy swapping. Connectivity includes a 4-port gigabit LAN switch permitting redundancy and bandwidth aggregation.
The Princeton DN-503AH-PDC 5TB NAS will go on sale in Japan from mid-December, no word yet on price. In comparison, the Buffalo NAS costs around $2,100.