Re: Optimize RAID0 for max IOPS?

[Dave Chinner <david@fromorbit.com>]

[ As a small note - if you are going to comment on the results table
from a previous message, please don't cut it from your response.
Context is important. I pasted the relevant part back in so i can
refer back to it in my response. ]

On Tue, Jan 25, 2011 at 08:39:00AM +0100, Emmanuel Florac wrote:
> Le Tue, 25 Jan 2011 10:03:14 +1100 vous écriviez:
> > > Version  1.96       ------Sequential Create------ --------Random Create--------
> > > A1                  -Create-- --Read--- -Delete-- -Create-- --Read--- -Delete--
> > >               files  /sec %CP  /sec %CP  /sec %CP  /sec %CP  /sec %CP  /sec %CP
> > >                  16   104   0 +++++ +++   115   0    89   0 +++++ +++   111   0
> > 
> > Only 16 files?
> 
> IIRC this is 16 thousands of files. Though this is not enough, I
> generally use 80 to 160 for tests.

Yes, you're right, the bonnie++ man page states that it is in units
of 1024 files. Be nice if there was a "k" to signify that so people
who aren't intimately familiar with it's output format can see
exactly what was tested....

As it is, a create rate of 104 files/s (note the consistency of
units between 2 adjacent numbers!) indicates something else is
screwed, because my local test VM on RAID0 gets numbers like this:

Version  1.96       ------Sequential Create------ --------Random Create--------
test-4              -Create-- --Read--- -Delete-- -Create-- --Read--- -Delete--
              files  /sec %CP  /sec %CP  /sec %CP  /sec %CP  /sec %CP  /sec %CP
                 16 25507  90 +++++ +++ 30472  97 25281  93 +++++ +++ 29077  97
Latency             23864us     204us   21092us   18855us      82us     121us

IOWs, create rates of 25k/s and unlink of 30k/s and it is clearly
CPU bound.

Therein lies the difference: the original numbers have 0% CPU usage,
which indicates that the test is blocking.  Something is causing the
reported test system to be blocked almost all the time.

/me looks closer.

Oh, despite $subject being "RAID0" the filesystems being tested are
on RAID5 and RAID6 with very small chunk sizes on slow SATA drives.
This is smelling like a case of barrier IOs on software raid on
cheap storage....

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com
--
To unsubscribe from this list: send the line "unsubscribe linux-raid" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html