(dammit, I can't make my psychedelic signature to work... I guess images aren't allowed, pfff)
What happened was I turned on the projector this week to find my HTPC frozen, and the drive light on solid. Nothing I did could unfreeze it, so I reset. Poof, it couldn't mount the array for /home (with 1.7TB of videos): bad superblock.
After much tearing of hair and gnashing of teeth I found that jfsutils had somehow been deinstalled. When I reinstalled it I again had access to the array. Fortunately no damage. I hadn't done anything remotely related to maintenance lately, so it's an infuriating mystery. Maybe I could have fixed BTRFS similarly, but I was too freaked out.
This is why I am moving toward a storage server for the garage, although this has shown me that RAID10 may not be the answer. I was shocked to find my filesystem unavailable, against everything I'd understood to be true about RAID10. I am alarmed, and looking for other options.