All storage fails: How to make a bootable backup for an M1 Mac

I've spent too many years in the storage industry to trust any data storage product, including Apple's. But even though a completely dead M1 Mac SSD will brick your system, there are still reasons to have a bootable backup. Here's why. And how.

To improve system security your M1 Mac won't boot if the internal solid state drive (SSD) completely dies. While there's been very little information released by Apple on their SSD architecture -- I'm hopeful this year's WWDC will rectify this -- we do know that SSD failures aren't always total. 

Why? Because, unlike disk drives, SSDs have fewer single points of failure. And more partial points of failure. Specifically, the NAND flash dies -- usually two in a chip package -- have been found by researchers to be the major source of SSD data loss.

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Apple Silicon recovery

A die failure might eliminate as much as 16GB of data on your SSD. So how do you recover on an Apple Silicon Mac?

M1 Macs introduced major changes and more redundancy compared to Intel Macs. There is macOS, macOS Recovery, and a new feature: System Recovery. 

MacOS Recovery can reinstall and recover your system. But what if macOS Recovery is not accessible? System Recovery is third option: a minimal macOS environment installed in a separate hidden container that can reinstall macOS and macOS Recovery.

But that's not all. Apple Configurator 2 also allows you to erase and reinstall macOS if System Recovery itself is not functional if you have another Mac to run AC2.

The four levels of recovery redundancy suggests that Apple engineers are well aware that SSD failures are a) potentially fatal and b) likely to be partial failures. But all of those recovery options take quite a bit longer than booting up from an external drive. That's a major reason a bootable backup may be a worthwhile investment.

Making a bootable backup

A bootable backup enables you to recover the quickest. But the process of creating one is more involved with Apple Silicon Macs.

The overview: 

  • Make a backup to a dedicated volume on an external drive 
  • Install macOS Big Sur on that backup volume 
  • Test that it works 
  • Then backup regularly to that same volume.

The order is important. Installing macOS Big Sur first won't work. I tried.

Use Disk Utility to create a new volume on an external SSD. Attach an external drive, bring up Disk Utility (Applications > Utilities), select Partition and choose the capacity, macOS file system (APFS or HFS+) and click Apply. A window will come up asking if you want dedicate the capacity or share unused drive capacity. Your choice, makes no difference for the backup.

Also: M1 MacBook Air review: After 3 months use, here's what I wish I'd known

Now, on the freshly created volume, I used Bombich Software's Carbon Copy Cloner to perform a backup of my M1 MacBook Air system drive. The default options work well.

Then install macOS Big Sur on that backup volume.

The hardest part is getting the macOS installer. They used to be downloadable from Apple's support pages, but no more. The fine folks at OS X daily figured it out

Open the Terminal (also in the Utilities folder) on your Mac and at the prompt paste in:

softwareupdate --fetch-full-installer

The system will search for the installer and then download it into your Application folder (look for Install macOS Big Sur.app). The installer is about 12GB compressed, and about 30GB decompressed, so have at least 50GB free space on your system drive.

Double-click on the Install macOS Big Sur app and direct it to install on the backup volume. Depending on the speed of the drive you'll be done in anywhere from 15 minutes to an hour. Test it by going to System Preferences and choosing the external drive as the Startup Disk and reboot.

Be aware that later backups will update user files, but not the OS version. Until you see a must-have feature in a newer version of macOS, there's no other reason to upgrade. Once you want to upgrade macOS, simply boot from the external drive, and use Software Update in System Preferences to perform the update.

The Take

The effort required to have a bootable backup makes it an option for people who rely on their Macs for a living. It's too much work for casual users who are the target demo for Apple's Time Machine.

But if your Mac time is money, there's no faster way to get up and running if there's less than complete SSD failure. Remember: all storage fails.

Backup, backup, backup.

Comments welcome.