@brian Thought some more about this – I’m sure you have already thought about it and are ahead of me.
What is the value of my backing up the Appdata/Roon folder? If I lose the OS and have to rebuild the machine, and salvage the library disks (maybe on a NAS, maybe backed up and I restore them), will a backup of the AppData/Roon folder work? I imagine not, probably contains a lot of machine specific stuff, absolute paths etc.
This is really the same problem as a cloud sync.
In both cases, you have to virtualize paths and other settings. Otherwise the recaptured metadata won’t be linkable to the library disk.
I agree that the Lightroom repair model is pretty unpalatable. The situation will probably be pretty rare, so maybe you could survive it. Or better yet, create an explicit Migrate verb, or Relocate Library verb. But one way or another, these situations have to be handled explicitly; disk level backup won’t work.
(I had never even thought about this. I think in terms of the sensitive data living on the data disks, not on the OS disk. Yes, I know there is Appdata. But I am so steeped in the cloud model, I think of machines as being stateless and disposable, all important data lives elsewhere, I rebuild machines all the time. The idea of important Roon data living on the OS disk hadn’t really occurred to me. I set my machine up with three hard drives provisioned to Storage Spaces, and then I created virtual volumes on that pool, some optimized for dynamic perf, others optimized for storage capacity at the expense of write perf. But you can’t boot from Spaces, so I set up a small SSD as a boot disk. But I keep thinking of this as being easily rebuilt. I have sync/backup of the data disks, but not of the OS disk. Ok, this may not be the norm today; it is the right model, machines should be ephemeral, but it may still be a rare model. But even so, the rebuild/cloud sync problem remains.)