Once all the volumes on 'diskN' are unmounted, you erase 'diskN' using the following command: sudo dd if=/dev/zero of=/dev/diskN id=$(mount | grep diskN | awk '') for i in $id do diskutil unmount '$i' done Remember to replace 'diskN' with the drive identifier for your drive.

Now you need to unmount all the volumes on the disk you want to erase. In my example I will be erasing 'diskN', but you need to substitute the correct drive identifier for your drive (such as 'disk0' in place of 'diskN'). Usually for a system with a single internal drive the identifier will be '/dev/disk0' (that is a zero), but you always want to verify the identifier. You need the '/dev/diskN' part from the previous command to identify the drive to erase. Identify the internal drives: diskutil list internal physical If you are booted into Internet Recovery Mode, use the following commands to identify and erase the internal drive: If you want to zero out the whole drive (all partitions/volumes), you can use the Terminal command line tool 'dd' to write zeros to the drive or volume. I'm thinking the Disk Utility 'Secure Erase' is assuming the drive is encrypted and only overwriting the encryption key for Filevault as suggested by This might a bug or poorly explained feature even when erasing a traditional hard drive without Filevault. I know Apple has changed Disk Utility and doesn't want to write zeroes to an SSD as it will wear them out quicker plus it cannot access all the blocks on an SSD.

Mac disk utility secure erase freezes