With a little help from Data Rescue, I was able to recover one of the two drives that went south yesterday. On both drives, it looks like the catalog got corrupted. How this happens on a journalling file system eludes me: I thought there was some security associated with that technology.
I have read around this topic and it sounds like Spotlight might be a contributing factor, either through it’s penchant for exercising the disk or through some associated data volatility.
The restored disk is where I keep a lot of backups and my online music collection, so that saves me some heartache. The lost disk might have a mechanical issue: it seems to spin up and down with an audible clicking noise, so I am going to test it out before I rely on it.
For search query purposes, the error -9972 is fixable. I couldn’t find anything but Data Rescue that would do it though. Frustrating that Apple’s own Disk Utility is unable to recover data from a corrupted disk.