External Hard Drive on Mac Won't Mount I can't mount an external hard drive. I have tried booting into Safe-Mode, mounting via Disk Utility and running First Aid, which won't proceed due to the following error:


  diskutil eject disk1 Volume timed out while waiting to eject


I have also gone through the steps oulined here and here, as well as using Clean My Mac.

Any suggestions?
There is a 3rd party app named Mountain which I use on my mac. It puts an icon in your menu bar and when you click on it. it will show a list of Volumes and you can mount or unmount them. The app is $6 but has a free trial period so you can test it and see if it solves your problem.  See image below.