Maximum SDHC write speed?

DDK

DDK

So it appears that not all SDHC cards are equal. I know that I need Class 10 but even then it seems there's a large disparity between brands and within brands.

I was looking at an Sandisk Extreme Pro and noticed that it was 90MB/s write speed which was the highest I've seen but is there a limit to what speed a camera can write to it? Would I be wasting money getting such an expensive card when the camera can only write at a maximum of 45MB/s or something?

Also, at what write speed do you start to see significant diminishing returns? Is there a vanishing point?

Although I'm specifically interested in the 600D/T3i, I'm happy for other cameras to be discussed or mentioned in reply.

Lastly, yes, I've Googled it and no, I wasn't satisfied with the conflicting answers and results I could find elsewhere.
 
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The highest I have personally seen with my very own eyes is 95mb/s. I use a 45mb/s card with my 600D and it works fine. You can get away with anything 30mb/s or higher I think it is safe to say.

Yes different cameras have different write speeds. I can't explain it perfectly and I currently can't find any sources, but say the 600D can take 3.5 pictures in one second (full 18mp resolution) and the 5D can take something like 6 in one second (not sure if actual figure: but it certainly takes more than 600D). It's faster at writing. Clearly you couldn't take advantage of that with a 15mb/s card.
 
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MileCreations said:
say the 600D can take 3.5 pictures in one second (full 18mp resolution) and the 5D can take something like 6 in one second (not sure if actual figure: but it certainly takes more than 600D). It's faster at writing. Clearly you couldn't take advantage of that with a 15mb/s card.
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This is all well and good for photos, but in terms of video, you hit a point where the camera is recording all 25frames at 1080p, or 60 frames at 720p and after that there's not much more for it to do. If you're finding a class 10 card works fine (I've found class 6 cards can cause issues in DSLRs), then I don't see the point in getting a faster write speed unless you specifically plan to take advantage of perhaps certain magic lantern hacks.

If the camera is writing 25fps to the card at 28Mbps, then getting a 95Mbps card is not going to give you any better performance than a 30Mbps card.
 
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Like Jax pointed out, under normal operation there's a point where a card won't feel any faster. If you do plan to use higher bitrates or RAW (if it makes it to the t3i) then you'll want as fast as possible!
 
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jax_rox said:
If the camera is writing 25fps to the card at 28Mbps, then getting a 95Mbps card is not going to give you any better performance than a 30Mbps card.
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PaulGriffith said:
Like Jax pointed out, under normal operation there's a point where a card won't feel any faster.
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Yeup, hence this post. What IS the maximum recording write speed of the 600D? Should I be going for 45MB/s or will 30MB/s be more than I'll ever need?
 
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The standard video in all the canon cameras currently maxes out at around 36-38 megabits/second, or just under 5 megabytes/second. As long as your card can sustain that write speed you won't see any performance increase in video mode with a faster card.

If you look at something like Sandisk's site where they list speeds you'll see they're all expressed in megabytes/second, not megabits. So even their class 6 'ultra' cards can run 20MB/second which is more than enough.

The only place you'll see a difference with higher speed cards (at least in regards to video performance) is when you are offloading footage. A full 32GB sandisk "Ultra" (20MB/second) holds about 90 minutes worth of footage and will take about half an hour to offload. A 95MB/second "Extreme Pro" would only take 5 minutes.

Whether that difference is worth the price is all about your workflow and the amount of footage you expect to be shooting. For most narrative work I'd say it's probably not a significant difference. For a run and gun documentary I worked on last year where we were flying from city to city each day we often found ourselves up at 2am each night (with 7am flights) wishing the cards would dump the day's footage faster.
 
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ItDonnedOnMe said:
If you look at something like Sandisk's site where they list speeds you'll see they're all expressed in megabytes/second, not megabits. So even their class 6 'ultra' cards can run 20MB/second which is more than enough.
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Interesting. So is the anecdotal evidence from people that say that they have problems with the class 6 cards a matter of mistaken perception by them? There seems to be a lot of conflicting reports. The general consensus seems to be to get a class 10 card but I have read many people claiming that class 6 do well enough for them. Then again, I've read a lot of people saying that they don't.

At this stage it's really a matter of price for me. Cheaper I can get something, the better but I also don't want to sacrifice quality for that price.
 
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There's the standard, and then there's the measured performance of the card. Looking at the wikipedia chart of SDHC speed classes it looks like Class 6 has a minimum performance of 6 megabytes/second. That's not a lot of headroom over the 5MB/sec the camera needs - any dip in write speed could potentially cause problems. The higher speeds of the SanDisk cards leave a lot more room for error.

So another brand might design their cards to just barely get over the minimum for a class 6 - which probably makes them cheaper. SanDisk probably designs their cards not to drop below the minimum - might cost a little more, but you can probably count on it a lot better. So I'd go by what the actual rated speed is rather than the class, as well as other people's experience with whichever particular brand you are considering.
 
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ItDonnedOnMe said:
The only place you'll see a difference with higher speed cards (at least in regards to video performance) is when you are offloading footage. A full 32GB sandisk "Ultra" (20MB/second) holds about 90 minutes worth of footage and will take about half an hour to offload. A 95MB/second "Extreme Pro" would only take 5 minutes.
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This will also be dependant on your reader as well - plug a fast card into a USB2 card reader and it will still be a lot slower, at least comparatively to a computer with a native card reader.
 
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My personal opinion is that your safest bet is getting an Extreme card, which writes 45mb/s, it's only an extra $20 to be safe. I've had trouble with cards that were only just above the needed speed
 
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