I have a MacBook Air 2017. Had an issue few days ago had to make a reset with the assistants of good old YouTube. Did the job okay took quite a while Now decided to use the Time machine that’s built in to the MacBook.. Will be using an external drive for the back up. One item is bothering me is when I go to make the first backup to the external drive will any part of that backup go to the internal drive of the MacBook. Or will everything be entirely on the external hdd connected via usb. Then maybe in a week or two I can connect the external drive and make another backup. My main concern is will it take up space on the internal MacBook hdd. As I don’t want to overload the MacBook drive. It’s a 256gb. Many thanks.hope someone can put my mind at rest with my dilemma. David.