So I was looking at my server’s various temperature measurements today, because I added a fourth hard drive a few days ago (this server is, among other things, a MythTV box, so I need lots of video storage capacity). I hadn’t looked at the temperature measurements in a while, because my Antec case has done an admiral job of keeping things cool enough in the summer. My case has a separate lower section for up to 4 hard drives with a dedicated fan, in addition to a fan in the back and one on top, all with three-position speed switches (and of course the CPU fan, which is variable speed too). An additional 4 hard drives can go in the upper front, but I have all four hard drives in that lower section.
I noticed that the hard drivers were running about 88°F, and they were generally rated for about 140°F. Pleasant surprise. It occurred to me that the fans have a much easier job when it’s generally about 70F in the office than when it gets as high as 87°F or so. So I turned down all the fans to low, and the hard drives are now running about 91°F (which is still very good) and the machine is that much quieter. The fans will last longer, too.
Lesson learned: Change the fan speeds with the seasons. I never thought about it before, but it seems obvious now.