[SyneRyder]

A few people here are disappointed that this post is about a tool that uses rsync. But the "competitor" link is more interesting - it points to the makers of SuperDuper!, a tool that makes bootable external backups. A couple of highlights:

"...it's important to note that Apple still hasn't released any documentation on the "proper" way to create a bootable APFS volume. An example of what they have in mind was released for the very first time when the High Sierra developer release came out a few months ago, but that's it. We basically have to make an educated guess about what they want."

and

"In particular, Apple has further tightened its System Integrity Protection process, and is completely denying access to some files on the startup volume, even when copying to a non-startup volume.... But since APFS is, again, basically undocumented... what could that backup be missing?"

http://www.shirt-pocket.com/blog/index.php/comments/news_on_...