Update: Slow parity check is a symptom of a 5.8 Kernel Bug where pre-Skylake CPUs get stuck at the minimum pstate MHz (often 800MHz). Scroll down in this thread for links to the associated Kernel bug and discussion. Otherwise, this link will jump you to my updated post in this thread.      I've been noticing that 6.9.0 has been slower than 6.8.3 for disk access when using dockers (also the high amount of disk reads on my cache even after making them 1MB aligned, but that's anothe