Extreme Performance Issues with v2.1.6 (and v2.2.3)

[nodarkthings]

So... I copied a 4GB file to a ZVOL, in the Finder, under v2.3.0 (10.14) and it's a lot better than it was (no big freeze even with a few apps launched, no file error), quite fast but 2.1.0 is still way faster.
EDIT 11/2025; the ultimate test is when I run a VM that sits in a pool, it's quite slow to boot, hangs a little and impacts the other apps. Back to 2.1.0: all becomes fast again...