Dual-Boot multiple MacOS versions - issues

[theWoosh]

I have recently setup a 12,2 mid 2011 27" iMac (with dual internal SATA SSDs and 32 GB RAM + Thunderbolt 1 USB 3.0 adaptor) to dual boot with it's native High Sierra plus (using OpenCore Legacy Patcher) Ventura.

High Sierra is installed on it's own 1TB SSD, while there are multiple APFS volumes on the second (2TB) SSD, and one of them contains Ventura.

They both boot up and work fine EXCEPT that High Sierra repeatedly crashes and reboots or freezes in the middle of the night while left on sleep (I was woken up around midnight last night by the boom of the startup noise from my office!).
I think that this is because of Spotlight indexing issues on High Sierra, as the only time I have been able to find anything in the logs, its about mds process repeatedly crashing (this before a system freeze on grey screen, so I could look at what was happening immediately before after restarting). There don't appear to be any reports in the logs prior to the system restarts, so I can't be sure.

I am aware of the fact that there are differences between the AFS versions on HS and newer macOS versions that can cause problems, so I initially excluded any Ventura- formatted APFS volumes from spotlight indexing and then stopped them from mounting at all in HS (with /etc/fstab), but still get this message 'Incompatible Disk - This disk uses features that are not supported by this version of macOS' on startup - what I would expect if HS is trying to mount volumes that were formatted in AFS by the newer Ventura, and possibly what is causing the spotlight indexing crashes - this might be one of the unsupported features perhaps?
I have also repeatedly (on HS) deleted the spotlight indexes and restarted spotlight, but the issues remain.

I guess there could be a problem for HS if Ventura has modified the file system for the existing HS-formatted volume that is shared by both OS versions?

I have kind of run out of ideas so would be very grateful for any useful info or suggested tactics for fixing the problem. Anyone out there with dual or multi-boot MacOS versions that has had similar problems?

Thanks for reading

 

[BrianBaughn]

The chances of someone here running a similar setup on a similar iMac are pretty slim.

I'd say that if the OCLP/APFS internal SSD is the sole cause of the High Sierra issue and can't be avoided the next thing to consider is moving it to external…for disconnection when running High Sierra. Can the iMac be booted via the Thunderbolt port (connected to an SSD via the USB3 adapter)? I don't know. Otherwise you'd be stuck with USB2 speeds.

 

[theWoosh]

I realise now (in retrospect after 3 months), that, like the proverbial fool, I have rushed in. Thought I would share my experiences as a warning to others (or, hoping against hope, an invitation to the Mac Gods to offer a solution)...

I wanted to keep the High Sierra system going so I could use my legacy apps, whilst installing the Legacy Patcher and more recent MacOS (in this case Ventura), to see if there were any problems and enable me to use current software.
Both systems do work, but I have had ongoing problems with the High Sierra side since I ventured on this voyage... As I mentioned before, I had no idea when I started, that there are multiple versions of APFS!

At the start I had multiple freezes and restarts which were hard to diagnose but seemed to have something to do with Spotlight processes. And of course there has always been that suspicious message 'Incompatible Disk. This disk uses features that are not supported on this version of MacOS' message. After finding out about the incompatibilities between different MacOS versions of APFS (including Volume Groups and Volume snapshots), I fixed the crashes by simply dismounting the Ventura volumes (that I could see in High Sierra) in /etc/fstab.

So all now seemed fine... Until a few days later, Spotlight just disappeared - nope, command+space didn't work either. It just wasn't running anymore. The Incompatible disk message still appears everytime I startup HS - I suspect it could be the snapshot volume or something that I can't see in DiskUtil but which is spookily still there in the background and causing enough problems with spotlight that it just gives up... Or something like that. Which makes the High Sierra system kind of unusable...

So I made a CarbonCopy clone of the Ventura system volume on a SATA SSD connected to my USB 3.0 thunderbolt USB 3.0/ESATA adaptor, thinking I would just erase the dodgy Ventura volumes and plug in the external when I want to boot Ventura. Then I hit a conundrum - how to delete the Ventura volumes when only Ventura can see them all? I'd have to dismount the Ventura system vol - sort of a reverse bootstrap... No problem - I can boot from my external drive and do it from there right? Well except that when I rebooted with the drive attached it didn't show up in the boot list (even though I had told CCC to do a 'Legacy Bootable' clone) - Maybe this old Mac just can't boot from an external USB3.0 drive (it's ROMs are a year older than the first iMac that did after all).

I don't want to risk trying to delete volumes/ volume groups from High Sierra Disk Utility and risk causing even more damage - I was warned not to try messing with newer OS APFS using older OS tools...

Maybe it's time for a reformat and reinstall - fortunately I made CCCs of the High Sierra install as well + time machine backups and cloud archive.... Heaven forbid, I might just have to buy a new Mac as well!