[ale] Confusing RAID Performance

[greg.freemyer at gmail.com (Greg Freemyer)]

Brian,

I'm curious too and went to your spreadsheet, but only the first 100
lines are showing up.  Possibly because I'm anonymous.

Can you move the fread and re-fread lines to the top of the spreadsheet?

Greg

On Wed, Feb 2, 2011 at 1:46 PM, Brian Pitts <brian at polibyte.com> wrote:
> I recently finished running iozone benchmarks comparing hardware and
> software RAID6 using 11 SATA disks on a server has 8GB of RAM.
> There was one part of the results that jumped out at me as not making
> sense. For the fread and re-fread reports, the perfomance of the
> hardware RAID increased when the test file went from 8GB to 16GB.
>
> Does anyone have a theory about why this might be?
>
> Here is the puzzling data. The top row is records sizes, the left column
> is file sizes. See how performance drops dramatically as we go from 4GB
> to 8GB, since the test file no longer fits in RAM, but then increases
> some for 16GB.
>
> Fread Report ? ?64 ? ? ?128 ? ? 256 ? ? 512 ? ? 1024 ? ?2048 ? ?4096 ? ?8192 ? ?16384
> 4194304 3499493 3559324 3485319 3338358 3353441 2864384 1614729 1537980
> 1469821
> 8388608 220831 ?216510 ?232010 ?325999 ?327661 ?332615 ?356501 ?357100 ?321870
> 16777216 ? ? ? ?644804 ?644335 ?629204 ?506989 ?624378 ?595963 ?596668 ?606618 ?652013
>
> Re-fread Report 64 ? ? ?128 ? ? 256 ? ? 512 ? ? 1024 ? ?2048 ? ?4096 ? ?8192 ? ?16384
> 4194304 3501556 3563106 3509425 3339554 3364700 3123160 1611168 1535767
> 1533804
> 8388608 234456 ?226453 ?242365 ?381102 ?386371 ?407422 ?389960 ?442331 ?384986
> 16777216 ? ? ? ?688988 ?688057 ?686493 ?686028 ?683425 ?687335 ?687437 ?686031 ?689457
>
> The definition of the fread test is "this test measures the performance
> of reading a file using the library function fread(). This
> is a library routine that performs buffered & blocked read operations.
> The buffer is within the user?s address space."
>
> I have more of the iozone output in this publicly-viewable spreadsheet
> if anyone cares to take a look at the rest of the results.
>
> https://spreadsheets.google.com/a/apidb.org/ccc?key=0AoW4-KM82tL9dDV3a3NMUmZ0aWozaFh6RWFRUGdaakE&hl=en&ndplr=1#gid=0
>
> --
> All the best,
> Brian Pitts
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Greg Freemyer
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