Yup it happened. Switched on my computer, the bios scanned the hardware and reported that one of my 2tb drives had failed it S.M.A.R.T checks. What? Was it missing a shirt and tie? I need details!!!
It was the alpha dive, one of two 2tb drives I have on my computer. Both carry the same files using SyncToy to mirror the contents every time I have finished a body of work. Beta drive was fine.
I ran a check on the drive and found that it had a bad sector, so I made sure that all my files were matched on the second 2tb drive and did a complete format of Alpha. I then ran a complete check disk and told it to fix anything it found. This took a few hours on a 2tb drive so I was reluctant to do anything on the Beta drive until Alpha was OK.
With Alpha returned to health I then copied all files back from Beta, ran check disk commands on both and made sure all was OK with my Lightroom catalog. Phew!
It was a bit of a shock to see Alpha screw up, both Alpha and Beta were bought at the same time and they are identical Samsung drives, but it can happen at any time. I am now thinking about second tier storage in case this happens again.