Re: Fio giving iops results that are equal to RAM speeds

[Erwan Velu <erwan@enovance.com>]

Le 07/05/2014 09:45, Kim Holmebakken a �crit :
> Hey,
>
> Im currently working on a bachelor thesis where I need to measure iops 
> on my storage solution.
>
> I have set up a "frontend" server(ubuntu server 13.10) which has zfs 
> on linux running, and is connected to an iSCSI RAID(SAN).
>
> When I use this command:
>
> fio --directory=/pool  --size=128M --direct=0 --fallocate=none 
> --rw=randrw --refill_buffers --norandommap --randrepeat=0 
> --ioengine=sync --bs=4k --rwmixread=100 --iodepth=16 --numjobs=16 
> --runtime=60 --group_reporting --name=4krandreadtest

[...]
> These values are extremly high and I suspect that these are the RAM 
> speed being returned to me.
>
> Is there anyway to get a more realistic result?

You do cached IOs (as direct=0), only 128M of data and everything into a 
file. As a result, yes everything is getting into the host's cache.

If you want to determine the ISCSI performance byitself, I suggest not 
using file but the block device and do direct IOs (direct=1).

If you want to keep your filesystem you have two options : enabling the 
direct=1 and/or making IOs at twice the size of your host memory.

Hope this helps,
Erwan