I briefly mentioned that the mirrored disks for my Runeaudio music player broke. I then compounded the issue by not RTFMing about the RAID enclosure- which also seems to have had a fault- with the result that I lost my FLAC collection.
I tried the excellent testdisk (which didn’t find any partitions) and photorec (which recovered files but no folder structure and with possible corruption), and decided I needed to bite the bullet, copy what I had on my phone back from there, and re-rip the rest. I’ve found as I have 2 CD drives, I can rip 2 together, and still use my laptop.

This post is looking like an exercise is open-source software promotion: the files were originally ripped to open source FLAC (and MP3 for the car) with open source abcde, recovery was attempted with open-source tools, the player itself is open-source, and there’s one more thing to add: I don’t want to have to do this *again*, so I need a backup solution, and preferably something that requires minimum intervention.
I already use Google Drive for other backup, and pay for a decent amount of space, so that seems ideal. The idea now is to use rclone on the Runeaudio device so that whenever I transfer new music to it, it ends up on someone else’s computer in the cloud as well, automagically. Initial tests on my laptop are encouraging:

So now it’s a case of installing rclone onto Runeaudio and seeing if it works.