SDHC cards - real speeds

Jul 01, 2013 3 Replies
D

I was planning to order another couple of SDHC cards.



Class 10 seems to be the fast option.



However I am seeing different speeds claimed for different cards.


claims up to 17BM/sec write speed.


claims 30MB/sec and UHS-1 compatibility.



So given that the Transcend is £8.45 and the San Disk is £10.04 you seem to get a lot of extra speed for not much more money.



Then again, the discussion (which I'm still reading)


seems to suggest that there may be limitations in the hardware/firmware and the Pi may also not be able to fully drive a UHS-1 card which requires a higher voltage.



So is it a waste of money getting the fastest possible card?



Cheers



Dave R


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M

I went for the Sandisk 30MB/sec, 8G card, and the speed difference is noticable over all other cards I have tried.

-- mrr

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T

What do you want it for?

AIUI Class 10 cards are fast for saving of large files, but utterly dire for random writes (small files or using as swap): Then again, the discussion (which I'm still reading)

UHS-1 requires a /lower/ (signalling) voltage (while keeping the supply voltage at 3.3V). AIUI the RPi does support that - indeed I think the Pi SD card interface is quicker than the BeagleBoard (TI OMAP). Note that thread is from 2012 while the drivers were still evolving - in particular the MMC was clocked at half speed for a while.

I suspect so, but for other reasons.

Theo

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D

On 01 Jul 2013 22:51:25 +0100 (BST), Theo Markettos declaimed the following:

Class 10 cards are rated for streaming a single file on freshly formatted media -- optimal for HD video. Classes 6/4/2 were rated on fragmented I/O (interleaved files, small files, etc.)

So yes -- it is possible that a Class 10 card may be a snail when used for something like an OS image...

Wulfraed Dennis Lee Bieber AF6VN wlfraed@ix.netcom.com HTTP://wlfraed.home.netcom.com/
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