Determining whether or not a SCSI disk is in use

[Garrett Cooper]

Hello again list,
    Just wondering if there was any way where I could possibly tie into 
the kernel or do something where I could determine whether or not a disk 
is currently 'in use'.
    Problem: I'm trying to spin down my disks periodically via a cronjob 
to save energy, reduce noise, and heat, and I don't want my disk to be 
spun down if it is currently in use. I do listen to music and watch 
videos for extended periods of time, so I'd rather not cause undue 
stress to the hard disks and cause the program I'm using on another 
machine to choke and die.
    Thanks!
-Garrett