Originally Posted by joemikeb
Originally Posted by artie505
How about reversing that procedure and cloning your data volume to an external drive that's already got macOS installed on it?

An interesting idea, but sadly one that does not work. I just tried re-cloning the data volume on my bootable Big Sur clone. The cloning process was very quick, but when I attempted to boot the re-cloned drive i kept getting a reversed ⌀ symbol and finally had to quit the process with the power switch. 😖

Ah-well, it was worth a try. I just wish it weren't going to take so long to re-install Big Sur on the drive after I erase it and once again clone the data volume to the drive. 🤷‍♂️ Although I don't really know why I am going to do that as the critical data stores will never be current on the cloned volume. But it is a shame to have such a fast external SSD sitting around unused. 🙅‍♂️

Here's my exchange with Mike Bombich:
Quote
artie: but that you can achieve a bootable volume by combining it with either a Time Machine or Recovery restore

Mike: No, Time Machine isn't required at all. An Internet connection is only required to download the Installer, which you've done already if you've installed Big Sur. Hang on to that Installer – drag it to some other volume to make a copy that the Installer won't delete. When you've finished installing Big Sur, run your CCC backup to get your Data-only backup created, then install Big Sur onto the backup. At that point you have a bootable backup, and presumably a backup of that macOS Installer as well. If Internet connectivity is a problem in your area, then definitely save a copy of the installer. (Addendum: Red text is contradictory, no?)

artie: Can I install Big Sur on an external drive and keep it current by cloning my internal data volume to it regularly?

Mike: CCC will keep the Data-only volume current, yes. Nothing copies the System volume – not CCC, not Time Machine, nothing nor nobody can copy it (yet), not even Apple. The only way to restore the system right now is to reinstall it.

FWIW, I'd wait on this one. There is no impetus to upgrade to Big Sur, and there are some lower-level things that are still not working correctly. The biggest problem right now is that the "Signed System Volume" is supposed to be cryptographically "sealed", but that seal is constantly broken. A volume with a broken seal isn't supposed to be bootable, but Apple has relaxed that requirement because the functionality doesn't work. You're in no worse shape than in Catalina where the volume lacks the seal altogether, but then there's also no advantage (security-wise) to upgrading just yet.
I've terminated the discussion because it's not reasonable of me to impose on Mike's time about functionality at a particular moment that may change in the next moment, not to mention the fact that I"m not even running Big Sur, so I can't run any experiments of my own.

The one thing I'm scratching my head about, and regret not having asked Mike about, is how Migration Assistant is dealing with this, and can it perhaps be used in place of CCC for some necessary functionality?

The new Great Equalizer is the SEND button.

In Memory of Harv: Those who can make you believe absurdities can make you commit atrocities. ~Voltaire