SUCCESS!! with OC 0.8.6 beta, thank you
@h9826790. I did a five chime NVRAM reset but I'm not sure if that was the secret. A mistake before booting is how I discovered it. I'm now wondering if perhaps I had been making an error when I was following the instructions in #1,314. Just in case others run into a similar problem, I will document what I did and the "mistake" which finally got it working. Apologies for the length.
First my initial experience was with using OC 0.7.3 to upgrade to BigSur on the same hardware except for it having a Nvidia GPU. I had no issues with that install, all went smoothly. I still have that volume. My current boot volume prior to this upgrade was OC 0.7.9 wich I believe I did back in June. At the time I needed a larger SSD and I believe I used CCC to clone the original OC 0.7.3 volume and then upgraded it to 0.7.9 by simply replacing files in the EFI folder as per instructions in post #1,314. That volume is an APFS volume with containers for BigSur and HighSierra. I have some software which requires me to boot HighSierra a few times a year.
Now as to my efforts this week, I initially tried to upgrade my oc 0.7.9 BigSur & HighSierra volume using oc 0.8.0, note that failure was probably due to my not doing "0.8.0 + 0.8.0.2". My system usually has a OC 0.7.9 SATA SSD in a SonnetTech PCIe card in slot two as the boot volume. The Users volume other than for one admin account is on a six disk RAID10 volume, 3 internal 3external, and an internal Time Machine volume. (Note, I also have SoftRAID drivers installed on the HDD volumes.) When upgrading appeared not to work, I decided to try a clean install on a different SSD which was inserted into one of the drive pays. During those attempts at the clean install, I would pull all the drives out and disconnect the external enclosures for fear of corrupting my RAID volume. However, there would be two SSDs one with OC 0.7.9 in the Sonnet PCIe card and one with a new OC to support Monterey in a SATA drive bay. All of those attempts, would result in the OC boot picker showing my original boot volume, its recovery volumes, and for the new Monterey volume a "macOS installer" volume and an EFI volume. Picking the EFI or "macOS installer" always got me back to the OC boot picker. I could boot from BigSur, HighSierra, their recovery volumes, but never from the installer or new volume. Yesterday, after trying 0.8.6 beta. The "macOS Installer" volume actually installed Monterey but didn't delete itself. So at that point I had a Monterey volume in Disk Utility and Finder. However, in the OC boot picker I had only "macOS Installer" and EFI volumes which I could successfully pick.
Today, I decided to change approaches. That is since I was able to clone and then upgrade my original OC 0.7.3 volume, that I would just start over from that volume. In preparation for doing that I moved the SSD with OC 0.8.6 and which previously had been displaying as "macOS Installer" and EFI volumes to my Sonnet card with the intent of erasing it after rebooting with the OC 0.7.3 BigSur volume in a SATA drive slot. In the process of removing all my HDD drives and moving the "macOS Installer" SSD to the Sonnet card, I actually forgot to insert the sled with the OC 0.7.3 volume into my MacPro before rebooting. Too my surprise, what came up was a single volume, which said "macOS Installer". I was puzzled at first and then saw the sled with the other boot drive sitting on the floor. However, I decided to give it a try. It worked! I had a clean install of Monterey. The only scare was that after the install it took two reboots to actually get into Monterey. The first reboot just took me back to the OC Boot picker, with a Monterey volume, and a Monterey recovery volume which after selecting Monterey for a second time actually worked. I was able to complete the upgrade process. Rather than putting one of the prior boot volumes back in the MacPro, I decided to use the TimeMachine backup to migrate information to the Monterey volume. That took longer than I would have liked but worked.
My questions at this point was my original error having two physical boot volumes with different versions of OC? I now suspect what was going on was that the OC which was running the boot picker was always the one on my OC 0.7.9 volume and not the new Monterey volume which I was trying to build using '0.8.0 + 0.8.0.2' or '0.8.6 beta'? Is it the first EFI to respond on the system bus? If so, I suspect it was always going to be the one in my Sonnet card. The last time I did an upgrade to OC 0.7.9, it was the new volume which I put in the Sonnet card because I wanted to move to a bigger SSD. Should I always been trying to reboot with a single boot volume in my MacPro after running the Monterey installer?
While I've only been running for about four hours it is working with my RAID volumes and all seems well. So hopefully it will continue that way. Unfortunately, my test was with a smaller SSD which I had laying around. Now I'll have to clone it to something larger but that can wait a few days while I'm playing around with Monterey.
Thanks to all of you in these forums who make it possible for neophytes such as myself to be able to do such upgrades and apologies for my dumb questions.
