Re: Measuring IOPS

[Martin Steigerwald <Martin@lichtvoll.de>]

Am Mittwoch, 3. August 2011 schrieb Martin Steigerwald:
> Am Mittwoch, 3. August 2011 schrieben Sie:
> > Martin Steigerwald <Martin@lichtvoll.de> writes:
[...]
> Does using iodepth > 1 need ioengine=libaio? Let�s see the manpage:
> 
>        iodepth=int
>               Number  of I/O units to keep in flight against the
>               file. Note that increasing iodepth beyond  1  will
>               not affect synchronous ioengines (except for small
>               degress when verify_async is in use).  Even  async
>               engines  my  impose  OS  restrictions  causing the
>               desired depth not to be achieved.  This may happen
>               on   Linux  when  using  libaio  and  not  setting
>               direct=1, since buffered IO is not async  on  that
>               OS.  Keep  an  eye on the IO depth distribution in
>               the fio output to verify that the  achieved  depth
>               is as expected. Default: 1.
> 
> Okay, yes, it does. I start getting a hang on it. Its a bit puzzling to
> have two concepts of synchronous I/O around:
> 
> 1) synchronous system call interfaces aka fio I/O engine
> 
> 2) synchronous I/O requests aka O_SYNC

But isn�t this a case for iodepth=1 if buffered I/O on Linux is 
synchronous? I bet most regular applications except some databases use 
buffered I/O.

-- 
Martin 'Helios' Steigerwald - http://www.Lichtvoll.de
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