Mac Mini can't unmount disk in Recovery Mode I need to wipe my Mac Mini and reinstall OS X. Booting into recovery mode (holding command+option+R), I try to erase the disk in Disk Utility but it says it cannot unmount the disk or gets stuck on "Unmounting disk" with an infinite loading progress bar.

I have also tried booting into the recovery partition by holding down option at launch, but the same applies.
Way by Terminal..

Use diskutil list in a Terminal instance to list all volumes and find yours.

Then do hdiutil eject disk?

Replace the ? with your disk number, making sure you are not trying to eject the main hard drive :) It is probably called "Disk1"

Here is a Sample when I insert a USB stick and run diskutil list



disk0 is my hard drive and I can NOT eject that one

disk1 is the USB and I cam eject it.