Hi, I hope it's ok to ask usage questions on this mailing list.
I have been using fio version 2.2.4 on a Fedora 22 server host to test
throughput on a 10 GigE LIO iSCSI block device. Up until this point I
have been testing with Direct I/O (direct=1) and writing directly to
the block device with filename=/dev/blah (no filesystem). I am seeing
bandwidth measurements that look reasonable. I next tried to repeat
this test with Buffered I/O (direct=0) and the bandwidth numbers are
way too large. Here is a comparison of the sequential write results
for various block sizes:
bs=4k => direct=95.945 MB/s, buffered=1475.4 MB/s
bs=512 => direct=495.328 MB/s, buffered=2637.333 MB/s
bs=2048 => direct=502.093 MB/s, buffered=2663.772 MB/s
As you can see the buffered bandwidth measurements are much larger and
don't make sense given that not more than 1200 MB/s can be transmitted
over a 10 Gbps network connection.
Now it's very likely I am doing something stupid and lack
understanding about how fio works. Someone please enlighten me!
Here is the script I have been using to collect my results for buffered I/O
#!/bin/bash
JOB_FILE=job.fio
cat << EOF > ${JOB_FILE}
[job]
ioengine=libaio
iodepth=\${DEPTH}
prio=0
rw=\${RW}
bs=\${BS}
filename=/dev/sdc
numjobs=1
size=10g
direct=0
invalidate=0
ramp_time=15
runtime=120
time_based
write_bw_log=\${RW}-bs-\${BS}-depth-\${DEPTH}
write_lat_log=\${RW}-bs-\${BS}-depth-\${DEPTH}
write_iops_log=\${RW}-bs-\${BS}-depth-\${DEPTH}
EOF
for RW in read write randread randwrite
do
for BS in 4k 512k 2048k
do
for DEPTH in 4 32 256
do
RW=${RW} BS=${BS} DEPTH=${DEPTH} fio ${JOB_FILE}
done
done
done
I have also tried running this script without the filename=blah
setting on an XFS formatted block device. I am still seeing inflated
numbers for this also.
Thanks,
Dallas
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