I have this WD 1TB external HDD that I'm running through eSata for about a year now.
For the last few months however the drive would get slow and disappear. I would have to shutdown. unpower, power on the drive, and boot up again for the drive to appear.
I know this happens when the drive is inactive for some amount of time (20-30mins).
All motherboard drivers, and bios are updated.
As of right now, I keep the drive from being inactive by seeding a torrent at 1Kb/s.