"Western Digital Caviar Green 2TB (WD20EADS) SATA hard drive is now supported by the entire TS-109/ 209/ 409/ 509/ 439/ 639/ 809 /809U-RP and the latest TS-119/ 219 Turbo NAS series."
"The maximum capacity can be extended up to a total of 16TB now on a TS-809 or 809U-RP' says Andy Chuo, Product Manager from QNAP."
Also, the latest compatibility list published April 22 has the WD20EADS in the list (and notably without any extra remarks!):
Myself, the server just arrived yesterday and I'm currently waiting impatiently for the RAID 6 rebuild to finish on 7x2TB. Currently simultaneously moving files from the front-USB backup (figured I may as well test it) off the final 2TB drive before I add it into the full RAID set.
At 7x2TB its showing me just below 10TB available ... yeah, RAID 6 means (n-2 disks) with each 2TB showing up only as 1.8TB. I just may decide to make it RAID 5 instead when all is done.