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DragonFly kernel List (threaded) for 2011-07
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Re: Blogbench RAID benchmarks

From: Francois Tigeot <ftigeot@xxxxxxxxxxxx>
Date: Mon, 11 Jul 2011 19:47:31 +0200

On Mon, Jul 11, 2011 at 10:23:33AM -0700, Matthew Dillon wrote:
> :The results were taken for one run only, they were not averaged.
> :Howewer, I repeated many times the tests for the RAID10 and RAID0 cases, and
> :the numbers were always consistent (7% variation at worst).
> :
> :No fancy disk scheduler was used. Besides newfs, defaults were used for
> :all commands.
>     Also, what blogbench command were you running?

The default: "blogbench -d /mnt/blogbench"

>     To get real results with
>     blogbench you have to remember that blogbench creates an ever-growing
>     data set and if the run isn't long enough the data set may not blow out
>     the buffer cache in one test, and blow it out in another, producing
>     radically different results.

There was some variation but not that much; Sascha suggested I also test
FreeBSD on the same hardware and it was a damn good idea.
The FreeBSD write performance curve follows pretty well the theoretical
performance increase of the different RAID sets.

>     I usually set --iterations=100 to force the blogbench data set to be
>     large enough to actually blow out the buffer cache.

Ok. If I get enough time, I'll do a third run with this parameter.

>     You should include the raw blogbench output as well.  It's a wall of text
>     but it is important because read activity can be very deceptive if a
>     filesystem bogs down on writes (because only writes expand the size of
>     the data set being read).  This makes the final numbers a bit problematic,
>     requiring additional analysis to really understand what is going on.

I'll keep the numbers in the future.

Francois Tigeot

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