Ejecting USB-Partitions on boot - works but not entirely

Question

I have an USB drive with four partitions. SuperDuper uses these partitions to back up my mac. Since SuperDuper is scheduled, I have the USB drive constantly connected. But quite frankly the noise of the USB drive is driving me nuts. So I eject the partitions every time I boot the mac up. SuperDuper is configured so that it mounts the partition when it is scheduled to back up and unmounts it again.

I am trying to find a way so that I do not have to manually eject the partitions. I have two methods that work. I edited the /etc/fstab file with the UUIDs and prevent the partitions from mounting and I tried the method of making a logon script that calls a "do shell script "diskutil unmount....."". Both methods work. The partitions do not get mounted. BUT the drive motor does not "turn off". I have to go into Disk Utility and eject the unmounted (light-gray) drive again for the USB drives motor to be quiet. It doesn't really matter which one of the four drives I choose to eject again, ejecting one does the trick.

I also noticed that if I automatically eject three of the drives on boot and then manually eject the fourth one that the USB drive powers down. So there seems to be a difference between ejecting via script and right-mouse click "eject".

Does anyone know why this is? Is there a way to eject the partitions so that the USB drive understands this?

Thanks

Answer 1

As Harald suggested the solution is to use "diskutil eject" not unmount.

For anyone else looking at this thread, my login script looks like this:

delay 5
try
   do shell script "diskutil eject \"/Volumes/MYPARTITION\""
end try

Thanks again!