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

From: Matthew Dillon <dillon@xxxxxxxxxxxxxxxxxxxx>
Date: Mon, 11 Jul 2011 10:23:33 -0700 (PDT)

: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.
:Francois Tigeot

    Also, what blogbench command were you running?  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.

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

    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.

					Matthew Dillon 

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