I have a ZFS pool of 8x NVME drives Kioxia CD6-R (Sequential 6.2 / 2.3 GBs r/w)
It's setup in a pool of 4x mirrors:
ZFlash:
mirror 1: nvme0|1
mirror 2: nvme2|3
mirror 3: nvme4|5
mirror 4: nvme7|8
If I install and run fio I get the expected performance of about 20GB/s read and 8GB/s...