NAS Optimizations for RockPro64

[MNtinkerer]

I don't use ZFS and I suspect my use case is much lighter than yours, so I don't think I can help, but a couple things come to mind:

Are you encrypting your disks? If so, could some of that work be offloaded to the RK3399's ARMv8 cryptography extensions by using the right configs & linux kernel module?

Could the driver for your PCIe/SATA card be contributing to CPU load? If so, perhaps switching to a card with a different chip could help? (Mine has a Marvell 88SE9235.)

Encryption is a good point. I don't understand enough about it at the kernel level, just how to use LUKS to lock an entire partition or ZFS encryption for a dataset.

Drivers seemingly are not the issue on PCIe as behavior is consistent despite operating system or any of the PCIe chipsets I have. This includes Marvell 88SE92xx which has had mainline Linux kernel support since kernel version 5. There are compile-time options for many drivers which is also worth exploring. Just not there yet with my Linux skill set.