Starko

A little progress update.

Thanks @JorgeB and @trurl and your suggestions.

Can confirm that NVME0 was dead, and NVME1 is barely hanging on.

My immediate worry at the start was that as no shares were listed in /Shares/, that I could end up losing everything. Even though I could see the data on the main array was still there, I didn't want to risk losing it by re-creating anything. Reading back, if I had said that in the first post, I would have saved myself a good deal of anxiety.

Reading this guide helped me understand that removing 1 disk from the cache pool was fine and supported. I connected an old (working) SSD via USB, and tried swapping both nvme0 and nvme1 with it. With nvme1 swapped out, Unassigned Devices helped me see that I could still access the data, even if in Read Only mode, and grabbed the Docker image and /appdata/ and copied via the webUI. With nvme0 swapped out, I could start the array, and while the cache pool would not mount, all the Shares re-appeared!

I changed all the shares to Primary location being Array and no secondary (i.e. leaving cache unused) - I'm unsure if this was needed (as the cache pool was not mounted) but it did make me feel a bit more comfortable.

As the pool was already unmounted, I figured it would be fine to remove it from the config. Did that, and everything is now running. As far as I can tell, no critical data has been lost. Most crucially, my HomeAssistant set up was saved - I was not looking forward to trying to rebuild that.

Fix Common Problems seems happy, and I've added both the Backup/Restore Appdata, and Cleanup Appdata plugins to add a bit more redundancy to this in the future.

Phew!