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Reinstalling MacOS from a wiped fusion drive Mac

dstreb

dstreb

macrumors newbie
Original poster
Nov 24, 2022
18
0
Fitchburg MA
Our Library has a fusion drive Mac that dates to 2018. I upgraded to Ventura, then found a critical application won't run on it, so I have to roll it back to Monterrey. I tried to back it up with Time Machine, but it wouldn't recognize my NAS network drive, my 1TB USB drive, or a 32GB USB flash drive, even though the Finder saw all three. So I went ahead and wiped the drive, figuring I'd reinstall everything anyhow.

I hold down <Apple>-R when booting and get to the menu with disk manager and try to reinstall MacOS High Sierra. When I try to select either of the two drives that show up, Macintosh HD and Update, it says they're both locked. When I exit and go to disk manager, First Aid complete fine when I unmount both of them, but if I leave them unmounted then Install MacOS doesn't see them. What am I doing wrong? How do I unlock the drives to reinstall the OS, and which one do I use?

And while we're on the subject, our Mac is wired to the network with an Ethernet cable. Why is there no provision to use the Ethernet babled network - only a wireless connection comes up, and our Library has a security page you have to approve in a browser, so the connection on the Mac fails. I have to use my phone as a wireless hotspot to get as far as I did! But that's a side issue. I really want to get this Mac going for the public.

I maintain PCs in a library environment, and this is our only Mac. Thanks for your patience.
 
Unless I'm mistaken, there was no "2018 iMac".
It's probably the 2017 release.

BE AWARE that to "go back" to an earlier version of the OS, you're going to need to COMPLETELY ERASE the internal drive, and start over.

So... get the internal drive backed up BEFORE you begin.

OS 12 Monterey seems to be here in the Apple Store:
apps.apple.com

‎macOS Monterey

‎macOS Monterey lets you connect, share, and create like never before. Enjoy new FaceTime audio and video enhancements, including spatial audio and Portrait mode. Get more done with powerful productivity tools like Focus, Quick Note, and Tab Groups in Safari. Work fluidly across your devices...
apps.apple.com

BE AWARE:
You can boot to internet recovery (NOT THE SAME AS "the recovery partition"):
Command-OPTION-R
or
Command-SHIFT-OPTION-R

HOWEVER, I don't believe either of these will offer Monterey.
The first key combo will offer Ventura
The second key combo will offer the OS that originally shipped with the iMac, which I believe is 10.12 "Sierra".

So...
If you want Monterey, I'm thinking that you're going to have to download a copy of the Monterey installer, then create a BOOTABLE flash drive, and use that to do the install.

You will need a 16gb (or larger) USB3 flash drive. Format it to "Mac OS extended, journaling enabled, GUID partition format".

You'll need a copy of the Monterey installer (get it from link above)

I would also recommend that you download BOTH of the following:
- Install Disk Creator
- DiskMaker X
Both of these are free utilities that will make creating the bootable flash drive easy.

I recommend BOTH of them, because if one doesn't work for you, you can try the other one.

Once you have the flashdrive ready, boot to it (hold down the option key at boot to invoke the startup manager).

At this point, I would recommend that you ERASE the internal fusion drive and "start over". Actually, if Ventura is on it, that's what you HAVE TO do.

SO... IS THE REST OF THE STUFF ON THE iMAC'S DRIVE BACKED UP?

Once the flash drive is booted, if the installer opens, QUIT IT for now.

Open disk utility.
VERY IMPORTANT -- go to the "view" menu and choose "show all devices".

I've never used a Mac with a fusion drive, so at this point you're going to have to look over at "the list on the left" and select the internal fusion drive, which I think will be "the top line".

Then click the erase button and erase it to APFS, GUID partition format.

Now quit disk utility and open the OS installer.
Start clicking through.
The Mac will restart one or more times, and the screen will go dark for a minute or longer with no other indication of activity. Be patient.

When done, you should see the initial setup screen "choose your language".

Now, connect your backup and click through. Use setup assistant to "bring over" the backed-up files.

Good luck.
 
Last edited:
Fishrrman said:
Unless I'm mistaken, there was no "2018 iMac".
It's probably the 2017 release.

BE AWARE that to "go back" to an earlier version of the OS, you're going to need to COMPLETELY ERASE the internal drive, and start over.

So... get the internal drive backed up BEFORE you begin.

OS 12 Monterey seems to be here in the Apple Store:
apps.apple.com

‎macOS Monterey

‎macOS Monterey lets you connect, share, and create like never before. Enjoy new FaceTime audio and video enhancements, including spatial audio and Portrait mode. Get more done with powerful productivity tools like Focus, Quick Note, and Tab Groups in Safari. Work fluidly across your devices...
apps.apple.com

BE AWARE:
You can boot to internet recovery (NOT THE SAME AS "the recovery partition"):
Command-OPTION-R
or
Command-SHIFT-OPTION-R

HOWEVER, I don't believe either of these will offer Monterey.
The first key combo will offer Ventura
The second key combo will offer the OS that originally shipped with the iMac, which I believe is 10.12 "Sierra".

So...
If you want Monterey, I'm thinking that you're going to have to download a copy of the Monterey installer, then create a BOOTABLE flash drive, and use that to do the install.

You will need a 16gb (or larger) USB3 flash drive. Format it to "Mac OS extended, journaling enabled, GUID partition format".

You'll need a copy of the Monterey installer (get it from link above)

I would also recommend that you download BOTH of the following:
- Install Disk Creator
- DiskMaker X
Both of these are free utilities that will make creating the bootable flash drive easy.

I recommend BOTH of them, because if one doesn't work for you, you can try the other one.

Once you have the flashdrive ready, boot to it (hold down the option key at boot to invoke the startup manager).

At this point, I would recommend that you ERASE the internal fusion drive and "start over". Actually, if Ventura is on it, that's what you HAVE TO do.

SO... IS THE REST OF THE STUFF ON THE iMAC'S DRIVE BACKED UP?

Once the flash drive is booted, if the installer opens, QUIT IT for now.

Open disk utility.
VERY IMPORTANT -- go to the "view" menu and choose "show all devices".

I've never used a Mac with a fusion drive, so at this point you're going to have to look over at "the list on the left" and select the internal fusion drive, which I think will be "the top line".

Then click the erase button and erase it to APFS, GUID partition format.

Now quit disk utility and open the OS installer.
Start clicking through.
The Mac will restart one or more times, and the screen will go dark for a minute or longer with no other indication of activity. Be patient.

When done, you should see the initial setup screen "choose your language".

Now, connect your backup and click through. Use setup assistant to "bring over" the backed-up files.

Good luck.
Click to expand...
When I do the command-option -R it gives me the option of installing High Sierra, but when I select the drives it says they are locked. When I do command-shift-option-R it offers Ventura, and sees one drive, and works just fine! Why would they appear locked with High Sierra and not Ventura?
 
"When I do the command-option -R it gives me the option of installing High Sierra, but when I select the drives it says they are locked. When I do command-shift-option-R it offers Ventura, and sees one drive, and works just fine! Why would they appear locked with High Sierra and not Ventura?"

Fishrrman's Mac rule #1:
A Mac that boots and runs is better than one that will not boot or run.

The Mac's entire concept of disk format has changed completely since High Sierra v. Ventura. You can't put HS on a drive that's formatted for Ventura.

I would suggest you create a bootable USB flash drive with a copy of the High Sierra installer on it.

Then, boot from the flash drive and erase the internal drive COMPLETELY, then see if you can get the install to go through.

Finally, if nothing is working for you, refer to "Fishrrman's rule #1" above...
 
So I need to get it running with Ventura, make a bootable flash drive, download a copy of Monterey, erase both the Fusion Drive and the hard drive, and install Monterey from the flash drive. Is that right?
 
"So I need to get it running with Ventura, make a bootable flash drive, download a copy of Monterey, erase both the Fusion Drive and the hard drive, and install Monterey from the flash drive. Is that right?"

I'm not sure if once you get it running with Ventura, that it will make a bootable flash drive for you.

I'm thinking that the tools I use to create bootable flash drives, such as DiskMaker X and Install Disk Creator, won't work under Ventura (not sure, I don't have Ventura).

It can also be done with terminal, but again, not sure if it will work.

My advice at this point is...
Put Ventura back on it.
If you can then figure out how to create a bootable flash drive, do it.
Then, boot, erase and try to install Monterey.
BUT... if all pathways trying to install Monterey fail, you'd better just "give up" on that app that won't run, and stick with a running Mac...
 
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