Ok you have misread the document because they say:
"Maximum storage capacity •
Only limited by number of hard drive bays (4) and USB ports (4). Example: Using
Using 500GB hard drives, maximum 4 terabytes (total supported capacity of all
all internal and external drives connected to HP MediaSmart Server)."
By that they mean Only Limited by the Number of Hard Drive bays & USB Ports & Hard Drive Sizes.. i.e. 4 bays 1.5TB Drives = 6TB or 4 bays 2.0TB + 3 1.5TB USB Drives would equal = 12.5TB or if you take the fact that you have 4 bays, and 4 USB Ports [3 on back 1 on front] & 1 eSATA port, that = 9x say 2.0TB would equal 18TB total.
When I redone my server to factory I swapped out the original 500GB drive for a 1.5TB I had on hand and replaced the drive then.
So you are bound to the number of drives you can attach and by their size limitations... thats it. Max it out man! Thats what I'm doing with what I got..though have plenty of room to go. Oh and remember if you use Grid Junction, you have to use 1 USB port for that to work.
Ok have a good time! Here's a good thread too on what people do w their servers... and mine is on the 2nd page - http://www.homeserverland.com/forums/f/52/t/1174.aspx
WHS EX475 4TB