The benchmark hard drive for DVR applications is the WD20EURS. It's specifically designed for 24/7 DVR applications and the WD10EURS (which is the exact same model only it's the 1TB version) is the drive that comes pre-installed from the factory in the HR34. Next to the WD20EURS is the WD20EARX which is identical with the exception of the transfer speed being 6gb/s on the EARX (the EURS is 3gb/s). No DVR is capable of faster than a 1.5gb/s transfer speed anyway, so it's irrelevant. The cache size does make a slight difference in pulling recordings from the memory, but that's it. The Green drives like the EARX have a 64MB cache anyway, so getting the Black model is meaningless where the cache is concerned. A 7200rpm rotational speed is complete overkill for a DVR application. Even 5400rpm is way more than what's needed for DVR applications. The Black Caviar drives are identical to the recommended Green ones with the exception of the rotational speed and the additional CPU. The increased 7200rpm rotational speed however runs several degrees warmer and is also nosier which makes the Black models a DISADVANTAGE in a DVR application. The second CPU in the Black models provides no advantage in a DVR application and does nothing to improve performance. You have to remember... we're not doing tons of power computing here guys, we're just watching television. So stop wasting time putting a 500 horse power engine in a Kia... it's still just going to be a Kia.