What is the difference between formatting a volume partition and a disk of which the volume partition is a part of? Ok suppose I am reinstalling macOS in recovery mode using a bootable usb stick so in recovery mode when I format macintoshHD should I format the volume partition I mean when you click on the downward arrow beside macintoshHD(The Disk) a second disk/volume partition appears below the name, should I erase that one or the disk itself what is the difference?﻿
The question answers itself - one is formatting (erasing) the whole disk and the other is formatting just the partition. If you have more than one partition, the first will wipe them all, the second will only wipe the one you selected.