After 12 hours, tried your tips and they worked like a charm. BIG THANKS!
Some extra notes for the curious:
System: iMac 27” Retina 5K Late 2015 (3TB Fusion Drive) running latest version of Sierra and about 2 TB of free hard drive space.
External 16 TB G-Speed Thunderbolt Drive Raid-0. Mac OS Journaled.
Takeaway: This just reeks of bad coding on Apple’s part, not bad configs.
Additional Installation Thoughts:
1. I didn’t check if you could run Disk Utility and First Aid in Internet Recovery Mode. Probably can, right? If so, saves time rebooting into standard Recovery Mode and then IRM. You can just do it in one step. Regardless, many will determine that this step is unneeded, but it is because any weirdness with the drive *may* have contributed to this problem in the first place. The repair process is usually quick, maybe a minute at most. So it’s highly recommended.
2. I had to wait only 8 minutes in Internet Recovery Mode, not 45. (I don’t think it’s installing twice, but downloading the installation media or updates, preparing for the installation, unpacking setup files or whatever etc.) This prep time likely varies because of each machine’s current download status, internet speeds, software needs, and so on. Again, my prep time was only 8 minutes.)
3. After the prep time above, the actual installation began. It initially announced an install time of roughly 45 minutes, I think it said 41 minutes. It then began the now classic install process and reached the same message: “Installation is in progress. Calculating time remaining...” But not to worry: It may look the same briefly, but it doesn’t hang on this message for long. It’ll stay this way and bounce to it intermittently, but it won’t remain there. Seconds to a minute or two, but NOT several minutes or hours like before. It’s ACTUALLY calculating this time, and you’ll notice the time remaining descending. WHEW!
4. Eventually, the message settles into a new one: “Installing: About XX minutes remaining”, XX of course representing actual numbers depending on how much time is remaining. Point is, the numbers do actual decrease. It will alternate between this message and the “scary” one about “Calculating time...” but only for seconds as it confirms/updates its calculations. However, it’s generally accurate at the beginning.
5: As you said: About 45 minutes, but for me, significantly less. When it got down to about “18 minutes remaining,” it actually rebooted, not in a failure, but in a “you won’t be needing the rest. Your newer model system is up to date. We’re done here.” And then I logged into High Sierra, and setting up the usual suspects: logging into icloud, etc. ALL SET!
Enjoy High Sierra. And guess what everyone will do next time: TimeCapsule Backup, after waiting a week from download availability.
