[ale] Confusing RAID Performance

[Jeff Hubbs]

Out of curiosity, how big are these drives?

On 2/2/11 1:46 PM, Brian Pitts 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
>