I am in the process of building 2 NAS boxes, both DNS343s, to replace my collection of USB discs. I upgraded both to v1.0.5 firmware. Populated with 1x 500GB, 1x 1TB and 1x 1.5TB discs, all from external USB drives I disassembled. I wanted to add the 4th disc in each so purchased 2x ST1500DM003 drives. These were recognised by each DNS343, but both failed to format after getting to < 10% and apparently stopping. I swapped these over and got the same result. I then fitted them to a couple of my now spare USB enclosures, then mounted and NTFS formatted in Windows 7. All worked fine. I therefore concluded: not compatible! Went out and bought 2x WD Caviar Green drives, added to DNS343s, formatted, setup shares, etc, all fine. Whilst annoying, I'm not heartbroken and will use the Seagate drives to replace smaller internal discs in my 'server' PC. I guess there's something common to these Seagate drives? Seems too much of a coincidence really.