Re: Measuring IOPS

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Am Mittwoch, 3. August 2011 schrieb Jeff Moyer:
> Martin Steigerwald <Martin@xxxxxxxxxxxx> writes:
> > - ioengine=libaio
> > - direct=1
> > - and then due to direct I/O alignment requirement: bsrange=2k-16k
> > 
> > So I now also fully understand that ioengine=sync just refers to the
> > synchronous nature of the system calls used, not on whether the I/Os
> > are issued synchronously via sync=1 or by circumventing the page
> > cache via direct=1
> > 
> > Attached are results that bring down IOPS on read drastically! I
> > first let sequentiell.job write out the complete 2 gb with random
> > data and then ran the iops.job.
> 
> If you want to measure the maximum iops, then you should consider
> driving iodepths > 1.  Assuming you are testing a sata ssd, try using a
> depth of 64 (twice the NCQ depth).

Yes, I thought about that too, but then also read about the 
"recommendation" to use an iodepth of one in a post here:

http://www.spinics.net/lists/fio/msg00502.html

What will be used in regular workloads - say Linux desktop on an SSD here? 
I would bet that Linux uses what it can get? What about server workloads 
like mail processing on SAS disks or fileserver on SATA disks and such 
like?


Twice of

merkaba:~> hdparm -I /dev/sda | grep -i queue
        Queue depth: 32
           *    Native Command Queueing (NCQ)

?

Why twice?

Thanks,
-- 
Martin 'Helios' Steigerwald - http://www.Lichtvoll.de
GPG: 03B0 0D6C 0040 0710 4AFA  B82F 991B EAAC A599 84C7
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