How to safely eject a volume when the icon has disappeared? I was using an external hard drive and the icon has disappeared (the program used to mount the volume hung so I stopped the process with diskutil unmountDisk /dev/disk3) - so now I do not know how to safely eject it. It's an old external hard disk, and I can feel it spinning when I put my hand on it, so I don't want to take any risks.
If a disk has been ejected via Finder and the icon has disappeared but you feel it hasn't yet, then here are some things you can try:

Does it show up in Disk Utility? If it does, eject it from there and if not, then it's safe to unplug.

In Terminal, diskutil list -- It the device is not listed then it's safe to unplug it. If it is listed use e.g. diskutil eject diskN where diskN is e.g. disk3, then follow it up with diskutil unmountDisk diskN.  If it doesn't unmount you can use: diskutil unmountDisk force diskN