NCQ enabled, 4 disks, 32 threads

heavy# zpool iostat 1
               capacity     operations    bandwidth
pool         used  avail   read  write   read  write
----------  -----  -----  -----  -----  -----  -----
...
test        40.0G  1.77T    194      0  22.3M      0
test        40.0G  1.77T    522      0  64.5M      0
test        40.0G  1.77T    548      0  68.0M      0
test        40.0G  1.77T    500      0  62.3M      0
test        40.0G  1.77T    507      0  63.2M      0
test        40.0G  1.77T    512      0  64.0M      0
test        40.0G  1.77T    529      0  66.1M      0
test        40.0G  1.77T    531      0  66.4M      0
test        40.0G  1.77T    508      0  63.5M      0
test        40.0G  1.77T    510      0  63.9M      0
test        40.0G  1.77T    523      0  65.4M      0
test        40.0G  1.77T    483      0  60.4M      0
test        40.0G  1.77T    492      0  61.5M      0
test        40.0G  1.77T    486      0  60.8M      0
test        40.0G  1.77T    525      0  65.7M      0
test        40.0G  1.77T    510      0  63.7M      0
test        40.0G  1.77T    499      0  62.4M      0
test        40.0G  1.77T    477      0  59.7M      0
test        40.0G  1.77T    522      0  65.3M      0
test        40.0G  1.77T    547      0  68.4M      0
test        40.0G  1.77T    573      0  71.7M      0
test        40.0G  1.77T    561      0  70.2M      0
test        40.0G  1.77T    579      0  72.4M      0
test        40.0G  1.77T    563      0  70.4M      0
test        40.0G  1.77T    570      0  71.3M      0
test        40.0G  1.77T    579      0  72.4M      0
test        40.0G  1.77T    577      0  72.2M      0
test        40.0G  1.77T    568      0  71.0M      0
test        40.0G  1.77T    554      0  69.3M      0
test        40.0G  1.77T    565      0  70.7M      0
test        40.0G  1.77T    576      0  72.0M      0
test        40.0G  1.77T    556      0  69.5M      0
test        40.0G  1.77T    587      0  73.4M      0
test        40.0G  1.77T    550      0  68.8M      0
test        40.0G  1.77T    548      0  68.4M      0
test        40.0G  1.77T    575      0  71.9M      0
test        40.0G  1.77T    581      0  72.7M      0
test        40.0G  1.77T    582      0  72.8M      0
test        40.0G  1.77T    565      0  70.7M      0
test        40.0G  1.77T    563      0  70.4M      0
test        40.0G  1.77T    541      0  67.7M      0
test        40.0G  1.77T    575      0  71.9M      0
test        40.0G  1.77T    564      0  70.5M      0
test        40.0G  1.77T    586      0  73.3M      0
test        40.0G  1.77T    569      0  71.2M      0
test        40.0G  1.77T    555      0  69.4M      0
test        40.0G  1.77T    568      0  71.0M      0
test        40.0G  1.77T    581      0  72.6M      0
test        40.0G  1.77T    567      0  70.9M      0
test        40.0G  1.77T    560      0  70.0M      0
test        40.0G  1.77T    552      0  69.1M      0
test        40.0G  1.77T    573      0  71.5M      0
test        40.0G  1.77T    585      0  73.1M      0
test        40.0G  1.77T    577      0  72.2M      0
test        40.0G  1.77T    573      0  71.7M      0
test        40.0G  1.77T    565      0  70.7M      0
test        40.0G  1.77T    558      0  69.8M      0
test        40.0G  1.77T    561      0  70.2M      0
test        40.0G  1.77T    554      0  69.3M      0
test        40.0G  1.77T    569      0  71.2M      0
test        40.0G  1.77T    581      0  72.6M      0
test        40.0G  1.77T    560      0  70.1M      0
test        40.0G  1.77T    589      0  73.6M      0
test        40.0G  1.77T    557      0  69.7M      0
test        40.0G  1.77T    589      0  73.6M      0
test        40.0G  1.77T    564      0  70.5M      0
test        40.0G  1.77T    556      0  69.6M      0
test        40.0G  1.77T    553      0  69.2M      0
test        40.0G  1.77T    573      0  71.7M      0
test        40.0G  1.77T    569      0  71.2M      0
test        40.0G  1.77T    562      0  70.3M      0
test        40.0G  1.77T    547      0  68.4M      0
test        40.0G  1.77T    563      0  70.4M      0
test        40.0G  1.77T    547      0  68.4M      0
test        40.0G  1.77T    580      0  72.5M      0
test        40.0G  1.77T    556      0  69.6M      0
test        40.0G  1.77T    566      0  70.8M      0
test        40.0G  1.77T    583      0  72.9M      0
test        40.0G  1.77T    568      0  71.0M      0
test        40.0G  1.77T    578      0  72.3M      0
test        40.0G  1.77T    567      0  70.9M      0
test        40.0G  1.77T    591      0  73.9M      0
test        40.0G  1.77T    566      0  70.8M      0
test        40.0G  1.77T    576      0  72.0M      0
test        40.0G  1.77T    570      0  71.3M      0
test        40.0G  1.77T    566      0  70.8M      0
test        40.0G  1.77T    560      0  70.0M      0
test        40.0G  1.77T    575      0  71.9M      0
test        40.0G  1.77T    577      0  72.2M      0
test        40.0G  1.77T    560      0  70.0M      0
test        40.0G  1.77T    545      0  68.2M      0
test        40.0G  1.77T    575      0  71.8M      0
test        40.0G  1.77T    543      0  67.9M      0
test        40.0G  1.77T    578      0  72.3M      0
test        40.0G  1.77T    553      0  69.1M      0
test        40.0G  1.77T    587      0  73.3M      0
test        40.0G  1.77T    566      0  70.8M      0
test        40.0G  1.77T    546      0  68.3M      0
test        40.0G  1.77T    552      0  69.1M      0
test        40.0G  1.77T    556      0  69.6M      0
test        40.0G  1.77T    544      0  68.1M      0
test        40.0G  1.77T    572      0  71.5M      0
test        40.0G  1.77T    566      0  70.8M      0
test        40.0G  1.77T    580      0  72.5M      0
test        40.0G  1.77T    549      0  68.7M      0
test        40.0G  1.77T    571      0  71.4M      0
test        40.0G  1.77T    552      0  69.1M      0
test        40.0G  1.77T    551      0  68.9M      0
test        40.0G  1.77T    560      0  70.0M      0
test        40.0G  1.77T    551      0  68.9M      0
test        40.0G  1.77T    534      0  66.8M      0
test        40.0G  1.77T    573      0  71.7M      0
test        40.0G  1.77T    528      0  66.1M      0
test        40.0G  1.77T    554      0  69.3M      0
test        40.0G  1.77T    558      0  69.8M      0
test        40.0G  1.77T    552      0  69.1M      0
test        40.0G  1.77T    542      0  67.8M      0
test        40.0G  1.77T    545      0  68.2M      0
test        40.0G  1.77T    553      0  69.2M      0
test        40.0G  1.77T    556      0  69.6M      0
test        40.0G  1.77T    159      0  19.9M      0