I got the phone call today - the MacMini is ready for pickup. I didn't recognise the phone number so I let it go to voicemail. I was impressed with the message. Detailed, professional, well-spoken. So far this incident, everything Apple has done has been exceptionally good.
I picked up the MacMini after work. The guy said the motherboard had been replaced and I would have no more problems.
I took it home and connected it all, and then booted up. Looked the same, so I just let it sit. I used it and watched the end of a movie. The only thing I noticed was that mds and mdworker were working overtime and really chewing into the CPU. Research shows that this is common when Backblaze is backing up. The name Backblaze kept coming up.
Mds and mdworker are part of Spotlight. They index the whole system and allow Spotlight to find files. I have never ever used Spotlight on any Mac over the years. I have used it once or twice on my iPad, but never on my Mac. I do not use it, I would rather not have it indexing my hard disk. And this is my media server. I don't need Spotlight to look for my files - iTunes does that and serves it up to my Apple TV. So I went looking for ways to turn it off. This seems to be a common desire and instructions were easy to find, In terminal, type this:
sudo launchctl unload -w /System/Library/LaunchDaemons/com.apple.metadata.mds.plist
Later, after Backblaze finishes running, I might want to turn Spotlight back on and I could use this:
sudo launchctl load -w /System/Library/LaunchDaemons/com.apple.metadata.mds.plist
I don't think I will want to do this, but I'll note it here just in case.
The MacMini has been running most of the evening, and no freezes or greyscreens have been experienced. I have used it with the Apple TV, BackBlaze is working away, I have backed up to it, and no problems. I will keep exercising it and hope it stays good.