@spinflip Try using recovery software like Recuva or WinHex. Best of luck. PS Always make backups. Boring but essential!
@iankenway I'll be trying that soon, and I have *most* of the files backed up but not quite all. But the larger thing I'm concerned about: what sort of failure mode wiped out 800gb of files without any warning, from what should have been a simple operation? And how often can I expect this to happen in future?
@spinflip I hope you're making progress with recovering your files. It can be a slow and fraught process. Maybe you could air your concern(s) on a Raspberry Pi Forum (I'm sure there must be one). If you have doubts about the disk's surface integrity, I would thoroughly recommend Gibson's SpinRite V6.00 Release 1. It's proved a life saver on several occasions. If you need more info or help about this, just let me know.
@iankenway thank you, and I do semi-regularly! This one's a bit difficult, as it's a media box with a few TB of video that could all be replaced without *too* much effort if needed