Seems like my disks in the RAID array aren't failing, it's the usb top-loading enclosure tthat's holding the disks that flaked out... I think. The dmesg logs indicated a usb disconnect right before RAID got unhappy. And it was both disks, not just one, in contrast to what I first saw.
Anyway, backups are up and running fine again. Horray for backups!
@cwebber What we really need is a World Restore Day.
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