Can't eject Hard Drive
sudo lsof /Volumes/myDrive to check current porccesses assoiciated with this Volume.
Then run the following starting with first and moving to the next if the previous did not work:
kill 2158 sudo kill 2158 sudo kill -INT 2158 sudo kill -KILL 2158
Also, sometimes the base command sudo lsof /Volumes/myDrive won't find anything. If that happens, try adding the +D argument (i.e. sudo lsof +D /Volumes/myDrive). That will do a top down scan of the disk. It'll take longer, but it should pick up anything that's causing the disk to be un-ejectable.
Find out which application is using external hard drive in order to eject it