I set up OMV over the summer to get all our family photos off facebook. I attached 2 1TB hard drives to my RPi3b+, and set them up to mirror each other (RAID 1). Shortly after that we had a power outage, and I was unable to access OMV from my computer. I wasn't terribly worried at the time, but after investigating, it looks like the disk does not show up under "Physical Disks" in the OMV GUI (edit: it shows up now that I've plugged that disk directly into the pi and not the powered USB hub). When I go to "File Systems", I see the file system, but OMV says it is not mounted and is "missing". I set the drives up to mirror each other specifically in the event a drive dies (they both power on and spin up when plugged into the pi, and when I plug the problematic disk into a manjaro machine, it can see it with the correct name, but cannot mount it). I've read through forum questions including this one: Missing Disk and this one: Software to read data from disk if OMV crash but nothing seems to answer the question of HOW to recover the data once one of the drives goes bad.
If anyone has any word of encouragement or a guide that will help, I would be extremely grateful. I've been at this for hours, and my wife is holed up in the bedroom crying her eyes out over the potential lost photos of our family.