I have two external hard discs connected through firewire 800 to a Macbook Pro. Usually I only work with one, so I unmount the other, which powers down. However, after some time the unmunted hard disk powers up for a while, then powers down. What is causing this activity? Can I somehow prevent it?
Preventing will be quite complicated, as not only a lot of system processes check for certain files on all hard drives regularly (think spotlight, time machine, etc.) and more often than not, opening a "choose file" dialog will spin up all hard drives, too, since the OS wants to leave you with a "fast" impression and thus spins up drives in advance.