Linux – Iozone is producing false results

iozonelinuxperformance

I am not sure why this is happening but these are totally false results:

    Children see throughput for 15 re-readers       = 12793134.62 KB/sec
    Parent sees throughput for 15 re-readers        = 12753940.84 KB/sec
    Min throughput per process                      =  515695.50 KB/sec 
    Max throughput per process                      = 1088000.75 KB/sec
    Avg throughput per process                      =  852875.64 KB/sec
    Min xfer                                        =  249856.00 KB

    Children see throughput for 15 random readers   = 12667347.75 KB/sec
    Parent sees throughput for 15 random readers    = 12613558.90 KB/sec
    Min throughput per process                      =  685239.00 KB/sec 
    Max throughput per process                      = 1318021.25 KB/sec
    Avg throughput per process                      =  844489.85 KB/sec
    Min xfer                                        =  274432.00 KB

The command executed:
iozone -i 0 -i 1 -i 2 -r 4m -s 512m -t 15

Best Answer

Your test size is 512 Mb. So you measure how your system respond to this load.
Your system have much more than 512 Mb of memory, so everything is read/writen to cache. So your results seems relevant.

If you want to test your disk, you have to use a much bigger dataset. Say twice the memory size. And flush the cache before each run: echo 3 > /proc/sys/vm/drop_caches

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