Get the following dialog when you try to eject an external drive on a Mac?

You can try identifing the program using the drive with the following command at a terminal prompt:

lsof | grep DODO

If this doesn’t help, type:

diskutil unmount “/Volumes/[drive name]”

The quotes are in case there is a space in name

This  donationware app is pretty handy: What’s Keeping Me