Reinstall macOS Big Sur after Erase Mac HD failed, Error…

Update:

I was able to use macOS Big Sur installer on external SSD and boot from it. Startup was < 30 sec. But 15+ hours later, after manually transferring user files and performing fresh installations of apps, it reverted back to the slow startup, although not quite as slow this time. Regardless, I was extremely disappointed. At this point I've given up. Now I am just waiting for the new iMac Pro. Hopefully migrating my user account to that will work.

Update:

Internet Recovery finally opened and this is what Disk Utility shows.

“Data, Data, Data..”. What does it mean?

Running First Aid on volumes. Now it’s frozen (spinning beachball).

Finally unfrozen. Next volume First Aid.

And finally Update volume.

Back to Reinstall macOS… but it shows Mojave! Why doesn’t it remember last macOS installed - Big Sur?

How do I download/install Big Sur? But if I install Mojave can I easily, immediately update to Big Sur without the typical user set up?

I can only update Mojave or to Monterey through Software update. I can try Monterey and migrate my user account from Big Sur TM backup or download Big Sur installer and see how that goes.

Updating Mojave. Amazing how fast everything is now.

I could have tried “Restore from Time Machine Backup” but I want to see if a clean installation of Big Sur will work (fix slow down issue) or not.

If SW Update still shows Monterey update only I’m going to use Safari to download/update Catalina installer and then Big Sur to see how that goes. Update by update, but with a clean install. Hopefully I will be back where I started and Big Sur will work properly (fast startup).

I’m taking the long macOS Recovery detour…

Restart took less then 30 seconds and login less then 5 seconds! I would still be waiting for Big Sur 10, 15, 30 minutes later for everything to settle down and be responsive.

Now it’s time for Big Sur installer update. This is it.

So far so good… 👍🤞

The initial Big Sur installer (11.6.1) was installed in about 30 minutes and restart was quick. It looks like this clean installation from Mojave to Big Sur might work.

The slow down issue in part might be related to the 15 years of macOS updates and migrating to new iMacs. I hope migrating my user account from TM backup doesn’t ruin it.

Now on to 11.6.4 update.

The 11.6.4 update is taking a bit longer and has gone through three Apple logo progress bars (third one being the longest). There was also a new update right after I hit Install Now.

It took about 17 minutes total to login screen but login was fast. The Desktop, Dock, Menu Bar, apps,.. all loaded right away. No lag in response. This is going well so far.

About This Mac still shows 11.6.4 but I’m sure there were two final updates with this version.

Now for the ultimate test; restarting it.

I celebrated too soon.

After using Migration Assistant to transfer my Big Sur User Account from Time Machine backup has returned my iMac back to its former self with slow restart/login (apps slow to respond,..etc). It's also caused issues with apps not opening (have to download/install again), Mail having to import email storage, and more. This macOS Recovery process is not easy. Too complicated. After erase/reinstall Big Sur I would have to reinstall/set up all apps,..etc, and manually copy all User Account files/folders from TM BU, which would take a long time. Doing a fresh install of apps and setting them up is one thing, but all the other app and system settings, preferences,... is too much.

Here are some screenshots of Disk Utility after migration. Not sure why that added back the "com.apple.os.update-##" volume.

Update:

I made a reservation with an Apple Service Provider in case I can’t resolve it Sunday. And if they can’t reinstall Big Sur due to some kind of HD failure, I will have them upgrade to SSD since Apple will not.

Update:

After giving up last night and shutting it down, it started up with “Internet Recovery” after turning on with CMD+R this morning.

Maybe that is a good sign. But it would seem something did not go right with erase and reinstall macOS Big Sur, that something is missing.

Unbelievable! It took 27 seconds to restart with Big Sur 11.6.4 and less then 5 seconds to login now compared to 10-15+ minutes before. 🎉🎉🎉

The lesson here is “Clean Install” with each major update or erase and reinstall from earliest macOS release for your Mac. I’m quite sure the 15 years of updates and migrating to new iMacs caused it.

Wish I had done this a year ago to avoid all the stress it has caused me. Thanks Apple.

Hopefully this will work for others having same slow-down issue after updating to Big Sur and Monterey. Now I feel more confident updating to Monterey.

Now to migrate my user account from TM backup. I hope that doesn’t ruin this moment. And fortunately I don’t have a lot of third-party apps, but I do have 300 GB of music to copy back.

So how do I Migrate my User Account from the previous Big Sur TM backup without ruining what I have done? Is there a certain way to perform it at this point? I only used my name for this new installation. I did not set up anything else with user account (no iCloud sign in,…etc).

Do I just connect the external TM SSD and use Migration Assistant to copy my account over? Should I change the current user account name to something else and then delete it afterwards, or does it matter? I seem to recall that Migration Asistant will ask you if you want to merge or replace account, correct?

Now I’m concerned that restoring my user account is going to copy over folders/files, settings,.. that mess it up or just cause other issues.

I’m surprised/not surprised no one has posted yet, or at least not a link to “How to use macOS Recovery / Erase Mac HD” or “How to Install macOS“. Maybe they’re waiting to see what happens.

I know others have tried something similar and it did not work for their Mac, but perhaps my approach (clean downgrade to/from Mojave) was different. Regardless, it’s a very bizarre problem for a lot of Mac users with either Big Sur or Monterey.

Should I change my current “Admin” user account (uncheck “Allow user to administer this computer”) before migrating? Will this cause an issue/conflict with login if I’m migrating another Admin user account? What about the current login password (same as before)?

I also had FileVault and Firewall turned on and my TM backup is encrypted.

Should I just ignore all of this and migrate my Admin user account over from TM backup?

I want this to be a clean migration. I don’t have enough experience with it (only with new iMacs during setup).

Should I use macOS Recovery “Restore from TM Backup” instead?