$ sudo fio --bs=4k --ioengine=libaio --iodepth=32 --size=10g --direct=1 --runtime=60 \--filename=/dev/vg-cache/slow --rw=randwrite --numjobs=1 --name=test
test: (g=0): rw=randwrite, bs=(R) 4096B-4096B, (W) 4096B-4096B, (T) 4096B-4096B, ioengine=libaio, iodepth=32
fio-3.12
Starting 1 process
Jobs: 1 (f=1): [w(1)][100.0%][w=475MiB/s][w=122k IOPS][eta 00m:00s]
test: (groupid=0, jobs=1): err= 0: pid=1634: Mon Oct 14 22:18:59 2019
  write: IOPS=118k, BW=463MiB/s (485MB/s)(10.0GiB/22123msec); 0 zone resets
[ ... ]
Run status group 0 (all jobs):
  WRITE: bw=463MiB/s (485MB/s), 463MiB/s-463MiB/s (485MB/s-485MB/s), io=10.0GiB (10.7GB), run=22123-22123msec