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Safely Reformatting an Apple Silicon Mac?

Luna Murasaki

Luna Murasaki

macrumors regular
Original poster
Jun 24, 2020
121
287
Purple Hell
I've always reformatted my Macs when a major new macOS release comes out rather than doing an upgrade install. I find I need to periodically reformat for organizational reasons and to clean out unwanted traces of old programs and this seems like a good time to do that.

I vaguely remember that in the very early days of Apple Silicon there was some kind of problem with reformatting M1 Macs that was leaving people with bricked machines they then needed to take to the Apple Store. I can't find clear info anymore on what the problem was and whether it was ever actually fixed.

I've owned a 16-inch M1 MacBook Pro for nearly a year now but this October is going to be the first time I will actually attempt to reformat it. I have a decade of experience with wiping Intel Macs and I am very comfortable doing that - maybe not in the best way, but in a way that seems to work well. But I don't understand if there's anything special/different I need to do with my M1 when compared with doing this on an Intel Mac. To be honest I am feeling a bit intimidated as I don't want to brick my computer.

My normal procedure with my Intel Macs:
  1. Download the installer program.
  2. Run the terminal command to create a bootable flash drive.
  3. Reboot the Mac into the installation environment on the flash drive.
  4. Open the Disk Utility within the installation environment.
  5. Completely delete all partititions on the internal storage drive. Change the partitioning scheme to MBR and back to GPT to completely erase any lingering cruft (I ended up with a stub of the Windows bootloader from boot camp once when I didn't do this part).
  6. Create a new blank APFS partition.
  7. Reboot the Mac and boot once again into the installation environment (skipping this step sometimes caused the installation to fail for me for unknown reasons so now I always do this).
  8. Select to install macOS on the blank partition.
If I did all this same stuff to my M1 Mac would it work out the same way? Or do I need to change how I do this to avoid a serious nightmare scenario?

I looked into the new "Erase All Content and Settings..." feature but it looks like that only deletes the user profile and not the actual operating system so it is not a complete solution to what I am wanting to do. I'm hoping to avoid leftover cruft from Monterey when I run Ventura if that's possible.

Thank you to anyone who can help.
 
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I reformatted mine in similar fashion to your description. Downloaded the installer, made the bootable USB, erased the disk in the boot-up settings, reinstalled from USB. Had no issues with this process.

(And this was the only way I fixed a weird Safari hanging issue I had every so often, no matter what else I tried)
 
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Luna Murasaki said:
I've always reformatted my Macs when a major new macOS release comes out rather than doing an upgrade install. I find I need to periodically reformat for organizational reasons and to clean out unwanted traces of old programs and this seems like a good time to do that.

I vaguely remember that in the very early days of Apple Silicon there was some kind of problem with reformatting M1 Macs that was leaving people with bricked machines they then needed to take to the Apple Store. I can't find clear info anymore on what the problem was and whether it was ever actually fixed.

I've owned a 16-inch M1 MacBook Pro for nearly a year now but this October is going to be the first time I will actually attempt to reformat it. I have a decade of experience with wiping Intel Macs and I am very comfortable doing that - maybe not in the best way, but in a way that seems to work well. But I don't understand if there's anything special/different I need to do with my M1 when compared with doing this on an Intel Mac. To be honest I am feeling a bit intimidated as I don't want to brick my computer.

My normal procedure with my Intel Macs:
  1. Download the installer program.
  2. Run the terminal command to create a bootable flash drive.
  3. Reboot the Mac into the installation environment on the flash drive.
  4. Open the Disk Utility within the installation environment.
  5. Completely delete all partititions on the internal storage drive. Change the partitioning scheme to MBR and back to GPT to completely erase any lingering cruft (I ended up with a stub of the Windows bootloader from boot camp once when I didn't do this part).
  6. Create a new blank APFS partition.
  7. Reboot the Mac and boot once again into the installation environment (skipping this step sometimes caused the installation to fail for me for unknown reasons so now I always do this).
  8. Select to install macOS on the blank partition.
If I did all this same stuff to my M1 Mac would it work out the same way? Or do I need to change how I do this to avoid a serious nightmare scenario?

I looked into the new "Erase All Content and Settings..." feature but it looks like that only deletes the user profile and not the actual operating system so it is not a complete solution to what I am wanting to do. I'm hoping to avoid leftover cruft from Monterey when I run Ventura if that's possible.

Thank you to anyone who can help.
Click to expand...

IMO erasing the System Volume is fairly pointless since Big Sur. Erase all Content and Settings erases the Data volume and leaves returns the machine to factory state with only the signed sealed System Volume. "Clean Install" by full erase are a relic from Mojave and earlier, when it made more sense. Unwanted traces of old programs will entirely be on the Data volume. The main reason for a Full erase/ Clean Install is if changing the OS version.

This article about the signed sealed System Volume in Big Sur includes this description:

"Once the System volume has been installed, a hierarchy of SHA-256 hashes is made to cover every file on that volume individually, and its file system metadata, in a hierarchical structure culminating in a single top-level hash known as the Seal. That is then verified against a value which is signed by Apple, providing a chain of trust for everything in that System volume. When that has been completed correctly, a snapshot is made of this System volume, which is specially designated as a System snapshot and blessed".

The System Volume is checked as above every boot and it fails you are directed to reinstall from Recovery. If It boots it is OK.
 
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Mike Boreham said:
... The main reason for a Full erase/ Clean Install is if changing the OS version. ...
Click to expand...

As I said in my opening post, I'm worrying about this now because of the upcoming OS upgrade to Ventura in October. I don't want Monterey cruft left over on my machine once I am on Ventura. That being said, from your description it sounds like Erase All Content and Settings is at least a suitable replacement for a traditional reformat in many cases - a lot more than I thought it was. That knowledge will definitely come in handy at some point, so thank you for that! 😊

fakestrawberryflavor said:
I reformatted mine in similar fashion to your description. Downloaded the installer, made the bootable USB, erased the disk in the boot-up settings, reinstalled from USB. Had no issues with this process.

(And this was the only way I fixed a weird Safari hanging issue I had every so often, no matter what else I tried)
Click to expand...

This is the main thing I was asking, so thank you very much! 😃
 
Luna Murasaki said:
As I said in my opening post, I'm worrying about this now because of the upcoming OS upgrade to Ventura in October. I don't want Monterey cruft left over on my machine once I am on Ventura. That being said, from your description it sounds like Erase All Content and Settings is at least a suitable replacement for a traditional reformat in many cases - a lot more than I thought it was. That knowledge will definitely come in handy at some point, so thank you for that! 😊
Click to expand...
OK but you don't need to do a full erase. The upgrade process will replace the signed sealed Monterey System Volume with a signed sealed Ventura one. Any Monterey cruft can only be on the Data volume. So Erase Content and Settings will get you where you want to be.

When I said the main reason was changing OS I was really thinking of downgrading.
 
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Mike Boreham said:
OK but you don't need to do a full erase. The upgrade process will replace the signed sealed Monterey System Volume with a signed sealed Ventura one. Any Monterey cruft can only be on the Data volume. So Erase Content and Settings will get you where you want to be.

When I said the main reason was changing OS I was really thinking of downgrading.
Click to expand...
Oh! I see. So it completely replaces the old system volume rather than upgrades? Because yes that would absolutely work the way I want if I just did an Erase All Content and Settings right afterward!
 
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This is a great post thank you. Coming from Windows and older macOS where I have had issues with the upgrades not applying correctly/leaving old stuff and causing conflicts. So I always do a format and reinstall.
 
Ethosik said:
This is a great post thank you. Coming from Windows and older macOS where I have had issues with the upgrades not applying correctly/leaving old stuff and causing conflicts. So I always do a format and reinstall.
Click to expand...

LOL I remember when I first learned how useless OS upgrades are. I attempted to convert my Windows XP installation to a Vista one back when Vista first came out. The Appearance properties screen was unusably broken at that point.

On modern Windows there is a feature where you can "Reset" Windows from the Settings app. If you select to wipe the drive and install a fresh copy of Windows from the Internet it's effectively a much easier alternative to a traditional reformat. When I first installed Windows 11, I began by upgrading my 10 install to make sure the license transferred over properly (no idea if this was actually necessary or not), then I immediately did a Reset after the upgrade was finished to blow away any remnants of Windows 10.

Edit: Correction, Settings app instead of Control Panel.
 
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I recently had a new Thunderbolt enclosure w/NVMe SSD create lots of trouble for me. It seems now like the ssd was faulty, and I'm expecting a replacement any day now. The drive would work fine until about 30% full, then self-eject and be very hard to re-format because of the self-ejecting.

It also had some strange effects on my internal drive, f.ex it would not show up in Startupdisk in sys prefs. So I decided to reinstall and at the same time get it from 11.6.3 to 11.6.8. Easier said than done. Lots of failures trying to erase in Disk Utilities from Recovery boot.

Then, I found, in the apple menu in recovery - "Erase this Mac". I selected it, provided apple-id and password, because the mac's still locked to it, and in a few seconds, the internal was erased. I installed Big Sur again, used Migration Assistant to restore my account from backup, and all has been good since.

I've been using macs and formatting, imaging, and shuffling mac systems for three decades, so I'm not new to this, but I'm still learning about the new 'system drive regime'.

Just thought I'd share.
 
Ben J. said:
I've been using macs and formatting, imaging, and shuffling mac systems for three decades, so I'm not new to this, but I'm still learning about the new 'system drive regime'.
Click to expand...
Three decades ago, Macs were still single-user and all you had to do was copy System: to any old drive and you could boot from it. Then, for at least the first decade of OS X, you could still build boot volumes anywhere – I had mine set to boot from an external but if the external was not mounted (most of the time) it would find the boot partition on the internal. Ah, the good old years of the cats.
 
Luna Murasaki said:
5. Completely delete all partititions on the internal storage drive. Change the partitioning scheme to MBR and back to GPT to completely erase any lingering cruft (I ended up with a stub of the Windows bootloader from boot camp once when I didn't do this part).
Click to expand...

that isn't a good idea. There is one partition on your drive that is "one true recovery" partition. Without "1TR" you don't have a recovery boot environment anymore. I'm not sure if the utilities protect against this (perhaps Disk Utility will stop you from shooting yourself in the foot this way,) .

There isn't a "boot off the internet" anymore. And to lower the security to boot off a non Apple drive you need to have "1TR" present to validate it. ( If the Apple internal SSD gets completely hosed then the Mac is bricked. ). If you have simply just "zeroed out" the internal drive you'll need another Mac to do a system recovery reset (via Apple Configurator) .
 
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