$ 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-3.1
Starting 1 process
Jobs: 1 (f=1): [w(1)][100.0%][r=0KiB/s,w=1401KiB/s][r=0,w=350 IOPS][eta 00m:00s]
test: (groupid=0, jobs=1): err= 0: pid=3104: Sat Oct 12 14:39:08 2019
  write: IOPS=352, BW=1410KiB/s (1444kB/s)(82.8MiB/60119msec)
[ ... ]
Run status group 0 (all jobs):
  WRITE: bw=1410KiB/s (1444kB/s), 1410KiB/s-1410KiB/s (1444kB/s-1444kB/s), io=82.8MiB (86.8MB), run=60119-60119msec