It's a Crucial MX500 1TB and some old Seagate 240GB model. They only had Steam/GOG game installs and nothing important fortunately.
I set up 11 on the gaming PC. All the drivers and app files transferred automatically (including obscure things like X-fi drivers) and the setup was surprisingly smooth. The BIB theme, Open Shell and Explorer Patcher make it look just like 10. There was one strange problem, 11 could not read two data SSDs at all that worked fine on 10, and behaved as if they were unformatted. Macrium could still read them so I just re-imaged them.
It would be interesting to check the event log around the time of the upgrade to see if any disk related errors/warnings pop up. It would be clever of an OS upgrade to mark non-essential volumes as read-only during the upgrade, somewhat less clever to forget to revert that change afterwards.
If it had been one SSD with this problem I would have suspected a fault, but with two at the same time seems incredibly unlikely... unless there's an underlying issue.
Always a good idea. For clean installs and upgrades.....I recall having some issue even when going from 8 to 10 several years ago. It was putting the recovery partition on some other, non-OS drive. It may be best to manually disconnect all non-OS drives when doing a Windows upgrade.
That's good advice but a bit of a PITA now that there's NVME slots on the motherboard and you need to practically tear down your PC to get to.Always a good idea. For clean installs and upgrades.