Larger block size leads to worse throughput

[AllenSun1024]

Please acknowledge the following before creating a ticket

• [x] I have read the GitHub issues section of REPORTING-BUGS.

Description of the bug: A larger block size leads to a worse throughput while a better throughput or maximum throughput(i.e., 115MB/s) is expected.

Throughput = 115MB/s, block size = 8KiB

Throughput = 96.5MB/s, block size = 16KiB

Environment:

Ubuntu20.04 Disk type = SATA, Disk size = 100GiB, File system = EXT4

fio version:

fio-3.16

Reproduction steps

[global]
name=seq-write-buffer-test
rw=write
bs=8k  # or 16k
size=4g
direct=0
iodepth=1
numjobs=1
ioengine=libaio
group_reporting
time_based
ramp_time=120
runtime=120

[job1]
filename=/dev/vde1