But if the enterprise drive costs twice as much as a RED or some other lower grade drive, wouldn't I be better off buying two cheaper drives and putting them in a mirror?
* an increased risk of data loss
* an increased risk of data unavailability
* a cost of $150/hr to get a tech on-site to replace drives
* you need to buy a larger/more expensive chassis
* you need to spend more on the controller to be able to compensate
This is really a moot point. If you're not clustering or otherwise building in tons of redundancy, you'll have higher availability and lower TCO buying from Dell/HP/whomever, and they'll bundle the right drives from the start.
If you are building a cluster, you're not going to take random advice from posters on Slashdot. Build out whatever you want, just know that SuperMicro has terrible support and warranties. Expect bad lots and don't forget to pay attention to firmware and settings.