Let's turn this around. How would you avoid this? Suppose that you are copying the file front to back. While you are doing this, an update comes in that chan

Let's turn this around. How would you avoid this? Suppose that you are copying the file front to back. While you are doing this, an update comes in that changes something in the front and back which refer to each other, while your copy is somewhere in the middle. The result is that you get a backup with a data structure in the back of the file referring to stuff in the front of the file that isn't there. Your backup copy is therefore corrupted. This problem is almost impossible to avoid. You just do the best that you can.