Western Digital’s Red series is definitely a success. It is superior to its predecessor in those parameters we could measure in our tests such as speed, power consumption and temperature. This advantage may be due to the progress that has been made in developing and manufacturing HDDs but the NAS-oriented firmware optimizations also contribute to its high performance, especially at writing. Talking about 4-disk NASes, their performance is actually limited by the Gigabit Ethernet interface rather than by the hardware platform or HDDs, so further progress can only be achieved in terms of lower power consumption and firmware optimizations for NAS-specific loads.
As we wrote above, it’s impossible to check out such an important parameter as reliability during a brief test session. But it is indicated by the warranty provided by the manufacturer (the MTBF parameter is synthetic and doesn’t reflect a drive’s reliability well enough).
So, the WD Red is surely a good choice for NASes. You only have to make sure that it is on the NAS’s compatibility list. Most NAS makers have already tested the Red series for such compatibility with their products. On the other hand, if you’ve already got a working NAS with WD Green drives, you shouldn’t hurry to upgrade unless you want to expand your storage capacity.
As for the price factor, the new series is currently slightly more expensive than the WD Green but much cheaper than the WD Black and RE series. Considering that the latter do not offer any significant advantages for NAS applications, the Red is obviously a better choice in this respect, too.