Purely a guess would be the caching on the sdds vs the nvmes - just to confirm, does what does ipref show as the link between systems?
Also, damn, that is a lot of data with no redundancy If you don’t mind me asking, what is the system for? First time I’m seeing TrueNAS used for raw speed.
You could also use @NickF1227 ‘s utility to test the raw performance of the pools, should at least help narrow down the bottle neck:
If you don’t mind me asking, what is the system for? First time I’m seeing TrueNAS used for raw speed.