Good question. The 0th-step answer is that the people using `dd` are generally going to be using all OS defaults, including for the filesystem. For what it's w

Good question. The 0th-step answer is that the people using `dd` are generally going to be using all OS defaults, including for the filesystem. For what it's worth, I know that dd'ing /dev/zero makes df show a smaller value. AFAIK, df (for ext4 in my case) isn't reading a logical abstraction of capacity as arbitrarily decided upon by a bunch of layers, but is straightforwardly reporting the free blocks on disk.