I have a miniMac M1 for M1 testing and development. I had set it up for dual boot with the original Big Sur partition that came with the machine and a new partition for Monterey. I've been using this for some months.
Summary:
After the steps taken below, and the subsequent steps to attempt to fix the problem, it became impossible to boot into the Big Sur partition. It seems that the System volume and the Data Volume had become disassociated making the partition unbootable.
I do see there might have been user error here; I had not gone into the Recovery mode on Monterey and enabled the possibility to boot from an external drive. Now, strictly speaking, both the Big Sur and Monterey partitions were internal since they were on the main hard drive. But could it have been that Monterey would not allow me to boot into Big Sur because I had not enabled the external boot possibility?
Detail:
I had always had the beta of Monterey installed, but because I needed to test a crash agains the release version of Monterey, I did the following:
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Set the startup disk to Monterey (something I'd never done before; I usually shutdown and hold the power button to select the boot drive.)
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I disabled the beta program in the System Preferences. System Update then showed the 12.0.1. I install that version and performed my tests.
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I then went to the System preferences to set Big Sur as the startup disk. I was surprised to see it wasn't listed (as it always had shown up there before).
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I ran Disk Utility / First Aid on the Big Sur partition, and then on the entire disk that holds both Big Sur and Monterey. They reported no problems.
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Then I then went into Recovery mode, and when I selected the Big Sur disk, it said "no users available for recovery". In other words, it couldn't see the data partition with the users on it.
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This seeming separation of System and Data partitions was confirmed whe I returned to the Finder after a reboot. I double-clicked the Big Sur partition, it only showed the System folder. It did not show "Users" or "Applications" or "Library"
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I went back to Disk Utility. It in fact showed the Big Sur data partition. When I chose File > Show In Finder the data partition showed up, with the "Users" or "Applications" or "Library" intact. So the Data volume was still there, but somehow the link between it and the System Volume seems to have been broken.
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Finally, I went to the Terminal, entered "cd /Volumes" and "ls -al". It showed the Monterey partition as a single directory. But the Apple M1 drive and it's Data partition were listed separately I sadly don't have a copy and paste, but something like this:
drwxr-xr-x 5 root wheel 160 Nov 18 07:58 .
drwxr-xr-x 20 root wheel 640 Jan 1 2020 ..
lrwxr-xr-x 1 root wheel 1 Nov 18 07:00 Monterey-> /
drwxr-xr-x 21 root wheel 672 Nov 18 00:10 BigSur
drwxr-xr-x@ 19 root wheel 608 Nov 18 00:08 Data
Any ideas what could have happened and how I can prevent it in the future?
Sincerely, Mark
