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As a preface, I want to mention that I'm aware that dual booting beta/bleeding edge versions of macOS alongside the stable public release can yield a situation where firmware is updated on Apple Silicon machines to match the firmware of the beta OS, which is a one way street, and can cause issues. I don't think that applies here as here, I'm asking about the right way to dual boot two copies of the same public, stable, version of macOS,

i.e. two copies of 14.7 Sonoma (which I need to test software in both production and vanilla environments) - the "base" system is the main production OS install, the "vanilla" system is the test second OS install.

Here's what I've done:

  1. Create a new APFS volume group in the root:

alt text

This adds one new volume that's 'installable' to, which looks like this in DiskUtility:

/dev/disk3 (synthesized):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      APFS Container Scheme -                      +994.7 GB   disk3
                                 Physical Store disk0s2
   1:                APFS Volume Macintosh HD            10.3 GB    disk3s1
   2:              APFS Snapshot com.apple.os.update-... 10.3 GB    disk3s1s1
   3:                APFS Volume Preboot                 6.1 GB     disk3s2
   4:                APFS Volume Recovery                936.4 MB   disk3s3
   5:                APFS Volume Data                    786.5 GB   disk3s5
   6:                APFS Volume VM                      1.1 GB     disk3s6
   7:                APFS Volume macOSSecondCopy         802.8 KB   disk3s7

After install disk3s7 is still present and disk3s8 has macOSSecondCopy - Data.

  1. I booted into the new macOS install (holding power button on the MacBook) - everything looked normal, didn't sign into any services/iCloud etc, just literally vanilla, ran some destructive tests which borked the install, now I want to remove.

  2. Back in the base environment, I simply deleted the entire macOSSecondCopy volume group, and it seems to be completely removed.

The only unusual thing I've noticed is that when I log into the vanilla install each time it prompts me to unlock the base installs volume and to enter my password.

Does this sound like a reasonable way to run, test and then delete a 2nd copy of the same version of macOS as the base, without causing issues to the Mac or my Apple ID/FindMy/Services etc?

If not, is there a cleaner way to dual boot two copies of macOS (same version or otherwise)?

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  • I’ve edited the title since “best practice” opens up many opinions like don’t do this, use a dedicated M1 mini for cleaner testing, use virtualization since Apple is adding support for Apple ID, iCloud, and you have a well researched and specific problem you’re facing. Let’s get that solidly solved and maybe have a follow on question later if several documented solutions need a “best practice” overview?
    – bmike ♦
    Commented Sep 19 at 13:02
  • that's good for me, I was really asking if what I'm doing sounds correct or hacky. From what I can gather it's reasonable - but keen to hear experienced thoughts, I've never dual booted a AS Mac. - I can't use a virtualised environment as I need to see GPU usage accurately. Tests also need to be on specific machine. There must be others that have dual booted two versions of macOS before though.
    – Woodstock
    Commented Sep 19 at 13:23
  • You are very correct. GPU passthrough and performance testing makes it tricky indeed on top of the Secure Enclave and new boot signing design for the hardware.
    – bmike ♦
    Commented Sep 19 at 13:33
  • totally agree, what's your take @bmike, look reasonable to you?
    – Woodstock
    Commented Sep 19 at 13:49
  • Looks reasonable, but all my direct experience is old so I just have second hand info from trusted peers on this. They all tend to decide hardware is cheap when they need solid test results. (Or use erase all contents liberally and have solid backups)
    – bmike ♦
    Commented Sep 19 at 14:03

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