They just skipped the special metadata device. It’s been a lifesaver on my proxmox backup server. It went from barely usable to pretty good. And that’s on first generation of HP microserver.

https://forum.level1techs.com/t/zfs-metadata-special-device-z/159954

The official wiki also has a ton of performance tuning tips, which worth checking out (especially the page on workload tuning).