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SDHC benchmark inconsistencies

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SDHC benchmark inconsistencies
« on: 06 / September / 2008, 02:23:26 »
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I'm using a 8 gb SDHC card and am getting some benchmark inconsistencies.
Actually, it is very consistent and repeatable, just wondering what is going on and if anyone else
is seeing this.

When I run the benchmark, the first time after a fresh format and chdk install
the "Write (Raw)" and "Write Mem" numbers are substantially slower than each subsequent time.
First time:
Write Raw: 3700
Write Mem: 3500
Second time and every time there after:
Write Raw: 11700
Write Mem: 12000


This is over a factor of 3. This is very repeatable. Once the camera is powered off, the low number returns again
as the first run of the benchmark.
It didn't matter whether the card was partitioned with a small FAT16 partition and big FAT32 partition or whether
the card was split down the middle with 2 FAT16 partitions.
It also didn't matter which build I used. (All best trunk vs Collab trunk).

I also noticed that if I took a single photo before I ran the benchmark, the numbers were also the faster numbers
and then after a power cycle the numbers stayed faster.

In all my other tests of non SDHC cards the numbers did not vary like this . They were fairly consistent.

It almost looks like there may be some kind of block boundary that is important when using SDHC.
Perhaps when not on this boundary, the low level write() code is having to do something additional
to preserve a partial block.
I have no idea what is going on, I just noticed the behavior.

Has anyone else seen this on a SDHC card?

BTW, this is on a SD850 using a 8gb Microcenter SDHC class 6 card.

--- bill

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Offline fudgey

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Re: SDHC benchmark inconsistencies
« Reply #1 on: 06 / September / 2008, 04:24:05 »
Now that you mention it, I think I saw something similar on my a570. Not this dramatic, though, just maybe 20% difference. Can't remember if it was just for SDHC or plain SD as well.

 

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