I'm not sure this is Time Machine. I know that in VMware Fusion, at least, there's an option to turn your monolithic disk image into a set of smaller individual

I'm not sure this is Time Machine. I know that in VMware Fusion, at least, there's an option to turn your monolithic disk image into a set of smaller individual files. If you turn this on, then Time Machine only has to backup the smaller part-image file that's changed. I know I've definitely seen Time Machine re-copying entire 10 GB virtual machine disk images before, with Parallels and VMware Fusion images, before I discovered this feature.