I'm testing a storage system under various configurations and am a little surprised by the results. We're using multiple VMs, each running fio against an EMC storage system. One of many tests is a repetitive (comparatively) small write test. Basically, a quick little script calls the same fio command a number of times in succession. Here's an example:
for num in `seq 20` do fio --name=randtest --ioengine=libaio --iodepth=4 --rw=randwrite --bs=8k --direct=0 --size=128m --numjobs=2 --output=/test/fio_output done
It's that simple. Now, the strange thing is that, according to Unisphere, read is exceeding write! On other, non-looping tests, the write was very high, read was very low, just as expected. Where is the high read level coming from?