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My Canon EOS 600D's class 10 SD card does not write out data very quickly and this results in buffering issues which can be seen when shooting 1080p@30fps video. Why can't the card keep up and what can I do to fix the problem?

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Probably another 'Class 10' card that actually performs to 'Class 10' standards instead of a phony 'Class 10' card. –  Michael Clark Jan 14 at 23:23
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@MichaelClark Well it is from transcend, I thought they were good enough? –  Andalur Jan 14 at 23:32
    
Transcend is well enough known to be 'cloned" extensively. I'd try some read & write speed tests using a PC and card reader to see the results. Then try a camera buffer full and see how long it takes to write a buffer to card (shoot high size stills until camera "stutters" then time how long until write-light goes out. –  Russell McMahon Jan 14 at 23:44
    
@Russell But I've bought this card from amazon and I'm absolutely sure it was no third party seller since it came in the "frustration free packaging" which is not used by third party sellers, I don't think amazon sells clones? –  Andalur Jan 14 at 23:52
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@Andalur - oops, sorry about the edit reversion mixup. I was trying to revert it to your original question as well and didn't see that you had the same idea, so I accidentally reverted it to the wrong thing. I've switched it back to where it originally was. –  AJ Henderson Jan 15 at 2:30
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4 Answers

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The class of a memory card often deals with the reading speed of the card, even if it should deal with the write speed. It is relatively common for a card to have much quicker read times than write times, but since the read time is fast enough, they slap a faster class label on it than it can actually write.

You will need to get a class 10 card that actually has high speed writing in addition to high read speeds. The best bet for checking this kind of thing is to read reviews of the cards and buy from reliable manufacturers that put the write speed in their spec. The spec can be important since SD card makers will often change the actual storage chips used without changing the part number of the card.

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According to sdcard.org the speed class refers to minimum write speeds. –  tenmiles Jan 14 at 23:52
    
@tenmiles - that may be the standard, but in the real world, read performance far exceeds write performance on most cards and they regularly only make their class on read performance. –  AJ Henderson Jan 14 at 23:53
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You don't mention which Transcend card you bought but the benchmarks here indicate that the write throughput performance of Transcend cards are a little under 10 Mbps (naively I assume this is true for their brand of SD cards but I could be wrong). Strictly speaking the SD Card class rating seems to imply 10 Mbps minimum for 1080p recording so that may partially explain why you are seeing that behavior with your camera.

If you can try other manufacturers, look at their benchmarks from them as well as reviews to see how it goes.

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I use an app called "Black Magic Disk Speed Test" to determine the read/write speeds of my various cards and disks which has the added benefit of also giving a go/no go status on the various standards (such as 1080p@30fps). Also, most of the time you can find user submitted images on Amazon that are screenshots of this (or similar) apps and see how users are actually reporting their speeds.

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It really is important that it be part of the spec the manufacturer shows too. SD card makers (even the big ones) will routinely change the actual flash memory in use on each card based on what supplies of flash memory are cheap at the time. –  AJ Henderson Jan 14 at 23:56
    
@Andalur - it would be good to use a separate reader to rule out the card reader in the camera as a bottleneck. –  AJ Henderson Jan 14 at 23:56
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You should mention that this app is mac only... –  Andalur Jan 14 at 23:57
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If you have success some times, and then not others, one source can be spikes in the time to write.

Some solutions are to make sure the card is recently formatted, thus all ready to write to, and no way near full, so there is plenty of space to lay down large chunks of data.

If you do the above and never have success, it could be too low a class card, and/or a fake card. I've seen reports of people buying 'fake' SD cards, that are just long end cards re-stickered. To test that a tool like the others mentions would be the trick.

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