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. 🤷â€â™‚ï¸ 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. 🙅â€â™‚ï¸
Here's my exchange with Mike Bombich:
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?
Thanks, artie505, for that informative post! What I have done in the past, and what I am hoping to do with a later version of Big Sur, is the following:
1. Download the latest Big Sur installer, and make a copy of it in another location (I suspect that will be V11.1. V11.0 will have too many bugs).
2. I have a Samsung 860 EVO 500 gig SSD, inside an Orico enclosure. I will use Disk Utility in Catalina to Erase and Format that entire SSD as APFS.
3. Do a clean, fresh installation of Big Sur V11.1 onto that external SSD.
4. Assuming Migration Assistant works the same, migrate/copy all needed files, folders, applications, settings, etc. from my OS 10.15.7 system.
5. Restart my Mac (it will be my late 2018 Mac Mini) from that external SSD.
That will be the start of my testing with Big Sur.
Now, the next "hurdle" will be when Big Sur compatible versions of SuperDuper!, Thunderbird, Onyx, LibreOffice, and Tech Tool Pro are released. Right now, of course, the
extremely critical one is SuperDuper!. The one that will take the most time, as usual, is Tech Tool Pro. Assuming all of that is complete (most likely in January, but possibly in February), my process would be:
1. Download the latest version of Big Sur (most likely V11.4 by that time), and make a copy of it in another location.
2. Perform my normal weekly disk cleanup/maintenance/backup tasks using Onyx, Tech Tool Pro, and SuperDuper!(SD). The backup/clone will be to an external SSD, and it will be my latest OS 10.15.7 (assuming no further updates to Catalina) system.
3. Restart my Mac from that just completed SD backup.
4. Use Disk Utility there to Erase and Format the internal SSD on the applicable Mac (I have 2 Macs, and thus will need to do all this twice).
5. Navigate to that most recent version of the Big Sur installer, launch it, and do a clean, fresh installation of OS 11.4 onto the internal SSD.
6. As expected, will be offered the opportunity to migrate/copy needed files, folders, applications, settings, etc. from that SD backup.
7. Once #6 completes, restart my Mac. Hopefully it will be successful with OS 11.4.
8. Finally, install the Big Sur compatible version of Onyx, and make an eDrive with Tech Tool Pro.
I am REALLY hoping all of that will still work. I will definitely visit this site to keep up to date, and inform others of my (hopefully) progress.
