meat

Absolutely nothing else is accessing it, I had turned off Docker and VMs, even killed network for a while to test to make sure of that, and yes, as I mentioned in my post, there were 69 read errors early on in the process and it ran smooth for several hours after that..   My cache pool was pretty full, all my isos, appdata, system, logs, and domains are on the cache pool and I was able to free up a good amount of space by removing some snapshots, and that made things go slightly better, it allowed me to turn the VMs and Docker back on, which makes sense, but it didn't really do anything for the parity sync.  I turned Docker and VMs back off to let it run a bit more but it would still top out at 2.0MB/sec max which appeared to be a write limitation.   Finally I just cancelled it, rebooted, and started over..  Wait to see if it slows again around the 50% mark.

well I went ahead and used the "New Config" option and I'm in the process of re-building the parity.  I'll look into finding a new USB drive.. hopefully one that lasts.