I've been having trouble with my hard drive going to sleep in Ubuntu 8.04. It seems that whenever I go off of AC power, the hard drive gets set to a very low power setting and a quick sleep mode, even after I plug it back in.

I'm able to reset it back to a usable setting by running:

sudo hdparm -B 252 /dev/sda
sudo hdparm -S 250 /dev/sda

Not sure if anyone else runs into this problem. I'll probably try and get this into an init.d script, but it really doesn't affect me all that often.