My sense was that the 20% speed advantage was as important or more than the small energy savings. Is that common for slower drives to handle data faster?
Maybe it's a side-effect of increased vibration for 7.2k drives? Hard drive performance drops in environments with high vibration. I could imagine that being a factor when you put 45 drives in a single server.
Anecdotal evidence, but I often find WD drives to be faster than their Seagate cousins, even at lower rotation speeds. I wonder if this is because of better firmware optimizations or because of higher platter density. Maybe it's both. Or maybe WD lies about their rpms ;)
Hitachi/HGST, now owned by WD, also makes really fast drives. Their 7200rpm 2.5" drives are the fastest laptop drives I've ever used, except SSDs.
The WD they use is a 5-platter HDD (1.2TBx5). The Seagate has 6 platters (1TBx6). The higher density means that the linear reads/writes are faster at the same spindle speed (more data passes under the heads in the same time interval). The interesting thing is that they are faster even at different speeds.
