Simple and Effective
iMac 5k 2015 - Was having aggrevating problem of having USB3 drives ejecting randomly, and gauranteed ejections when the display would sleep. Sleep in prefrences was turned off, Hard Drive sleep was turned off.
I decided to try this little app utility, under suspicion that the system would go into some sort of sleep mode and even though hard drive sleep was off, also force hard drives to sleep/disconnect.
It has fixed my external hard drive ejecting problems completely. Been using for what must be a week and not one random drive ejection.
Thanks!
marsofearth about Sleep Control Centre, v1.2