line, your entire pool is capable of 150MB/s - not each disk.
This seems, as the kids would say, "a little sus" as my 2-way mirror-pool can beat those numbers, and you have a four-disk stripe which should theoretically be able to push a much higher rate of throughput.
Code:
root@freenas:/mnt/MirrorVolume/test # fio --name TEST --eta-newline=5s --filename=fio-tempfile.dat --rw=randwrite --size=50g --io_size=1500g --blocksize=128k --iodepth=1 --direct=1 --numjobs=1 --group_reporting --runtime=60
TEST: (g=0): rw=randwrite, bs=(R) 128KiB-128KiB, (W) 128KiB-128KiB, (T) 128KiB-128KiB, ioengine=psync, iodepth=1
fio-3.0
Starting 1 process
TEST: Laying out IO file (1 file / 51200MiB)
Jobs: 1 (f=1): [w(1)][13.1%][r=0KiB/s,w=148MiB/s][r=0,w=1184 IOPS][eta 00m:53s]
Jobs: 1 (f=1): [w(1)][23.0%][r=0KiB/s,w=141MiB/s][r=0,w=1125 IOPS][eta 00m:47s]
Jobs: 1 (f=1): [w(1)][31.7%][r=0KiB/s,w=155MiB/s][r=0,w=1243 IOPS][eta 00m:41s]
Jobs: 1 (f=1): [w(1)][42.6%][r=0KiB/s,w=133MiB/s][r=0,w=1064 IOPS][eta 00m:35s]
Jobs: 1 (f=1): [w(1)][52.5%][r=0KiB/s,w=127MiB/s][r=0,w=1015 IOPS][eta 00m:29s]
Jobs: 1 (f=1): [w(1)][62.3%][r=0KiB/s,w=146MiB/s][r=0,w=1166 IOPS][eta 00m:23s]
Jobs: 1 (f=1): [w(1)][71.7%][r=0KiB/s,w=139MiB/s][r=0,w=1115 IOPS][eta 00m:17s]
Jobs: 1 (f=1): [w(1)][81.7%][r=0KiB/s,w=126MiB/s][r=0,w=1010 IOPS][eta 00m:11s]
Jobs: 1 (f=1): [w(1)][90.2%][r=0KiB/s,w=141MiB/s][r=0,w=1126 IOPS][eta 00m:06s]
Jobs: 1 (f=1): [w(1)][100.0%][r=0KiB/s,w=141MiB/s][r=0,w=1128 IOPS][eta 00m:00s]
TEST: (groupid=0, jobs=1): err= 0: pid=54757: Fri Sep 16 15:15:41 2022
write: IOPS=1290, BW=161MiB/s (169MB/s)(9681MiB/60001msec)
clat (usec): min=27, max=340794, avg=767.57, stdev=3622.40
lat (usec): min=30, max=340797, avg=771.09, stdev=3622.46
clat percentiles (usec):
| 1.00th=[ 30], 5.00th=[ 31], 10.00th=[ 58], 20.00th=[ 68],
| 30.00th=[ 79], 40.00th=[ 86], 50.00th=[ 91], 60.00th=[ 101],
| 70.00th=[ 113], 80.00th=[ 586], 90.00th=[ 1762], 95.00th=[ 4080],
| 99.00th=[11076], 99.50th=[12649], 99.90th=[16057], 99.95th=[22152],
| 99.99th=[99091]
bw ( KiB/s): min= 1024, max=2324409, per=99.53%, avg=164440.47, stdev=212517.62, samples=119
iops : min= 8, max=18159, avg=1284.18, stdev=1660.30, samples=119
lat (usec) : 50=9.45%, 100=49.57%, 250=15.24%, 500=3.34%, 750=7.23%
lat (usec) : 1000=1.28%
lat (msec) : 2=4.52%, 4=4.25%, 10=3.71%, 20=1.34%, 50=0.04%
lat (msec) : 100=0.01%, 250=0.01%, 500=0.01%
cpu : usr=0.86%, sys=7.33%, ctx=91342, majf=0, minf=0
IO depths : 1=100.0%, 2=0.0%, 4=0.0%, 8=0.0%, 16=0.0%, 32=0.0%, >=64=0.0%
submit : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
complete : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
issued rwt: total=0,77448,0, short=0,0,0, dropped=0,0,0
latency : target=0, window=0, percentile=100.00%, depth=1
Run status group 0 (all jobs):
WRITE: bw=161MiB/s (169MB/s), 161MiB/s-161MiB/s (169MB/s-169MB/s), io=9681MiB (10.2GB), run=60001-60001msec