Thanks for the suggestion! I set it to 4 and restarted.
It’s obviously making a difference, as both CPU and disk IO are higher, but the difference is only by a few percent. CPU is around 15-16 percent, making brief excursions to 18-19%. Disk IO is increased to around 60-80 MB/sec.
My hunch is that it’s IO bound at this point. The disk’s manufacturer’s sustained transfer rate spec is 110MB/sec, but of course there may be a lot more going on here. Might see some benefit from trying a newer/faster drive or testing on an SSD.
Anyway, performance issues aside, I’m still curious about why it’s failing at the end, and what I can do to diagnose the problem.