Procedure looks to be all correctly done, and honestly I could never imagine how it could be user error since any deviation from the procedure will abort it or not even work, the sync errors start right after the 8TB mark, and curiously they are not on every block, it's every third one, I'm going to try and duplicate this with similar size disks to see if I can find out what's triggering it, if I can't I'll ask Tom to take a look.