I had a weird problem at work (going back quite a while now as I haven’t touched this block in months/years!).
We have a 750gb Freeagent Pro External Hard Drive (USB) which was connected and mounted correctly on our linux server. I tried, and failed, to run backups to the drive for a couple of days until I figured that for some reason after about 15 minutes of it being powered up, it would go dead, unmount itself and fall over.
Eventually I decided to have a hunt around on the internet and found that this specific drive has a sleep feature. Basically, after 15 minutes (i seem to recall) of no-use, it would go to sleep. It seems to have been configured to work on a windows based machine that may feed it some information or some such, as apparently when attaced to Linux, it didn’t care whether or not it was doing anything, it would just go to sleep!
After a while I found (stumbled upon) this article – http://alienghic.livejournal.com/382903.html and sdparam – http://packages.sw.be/sdparm/
Basically, all credit to Diane from there on. You use sdparam to change the standby flag on the drive, basically disabling the feature entirely.
Problem solved.
