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6D needs a fast enough SD card for RAW @ 4.5FPS


After reading some reviews about issues with (secondary) SD card controller in famous 5D MarkIII camera, I decided to test the one in my new 6D camera.

Speeds tested with same composition and lighting (poor tungsten), same frame settings: exposure 1/200 @ f/1.6 on iso 800, object of shooting was my window mounted room air conditioner (LOL, I know ha ha!):


Since I already spent some time on preparing the information for myself, I thought I'd share it here 🙂

File sizes with approximate write bandwidth at camera's max 4.5FPS (continous shooting mode):
RAW 20M 5472x3648 - file size of 22,814 KB ~ 100.2 MB/s
mRAW 11M 4104x2736 - file size of 16,581 KB ~ 72.9 MB/s
sRAW 5.0M 2736x1824 - file size of 11,228 KB ~ 49.3 MB/s
L high 20M 5472x3648 - file size of 5,303 KB ~ 23.3 MB/s
L medium 20M 5472x3648 - file size of 2,488 KB ~ 10.9 MB/s
M high 8.9M 3648x2432 - file size of 2,463 KB ~ 10.8 MB/s
M medium 8.9M 3648x2432 - file size of 1,090 KB ~ 4.8 MB/s
S1 high 5.0 2736x1824 - file size of 1,470 KB ~ 6.4 MB/s
S1 medium 5.0 2736x1824 - file size of 643 KB ~ 2.8 MB/s
S2 2.5M 1920x1280 - file size of 766 KB ~ 3.4 MB/s
S3 0.3M 720x480 - file size of 155 KB ~ 0.7 MB/s
*approx write bandwidth calculated with formula (FILE_SIZE_KB * 4.5)/1024, results in MB/s rounded up

from observation it seems that file sizes can grow by around extra 50% for JPG (Large high quality) or sRAW at certain composition & light scenarios.

Maximum file sizes I've seen were 27,800 KB for RAW (calling for over 122 MB/s write speed in 4.5FPS continuous shooting mode) and nearly 8 MB for Large JPG in high quality (equivalent of 35.1 MB/s in continuous shooting mode). Former one was no go with Sandisk Extrme SD (bus afte 13 frames), the latter went through no problem for around 30 secs (over 130 frames).

phew ... bottom line is I was able to shoot continuously all kinds of JPG frames infinitely (tested up to 30 secs) with my Sandisk Extreme 45MB/s SD card ... however that's way too slow for any kind of RAW frames - literally after 13-16 frames you will see a "BUSY" message and shutter speed will drop to 0.9FPS until you release the shutter button and let the camera save the buffer to card, then you can repeat.

I was actually thinking of buying the fastest SD card on the market I could find, but gave up after I came back finding only Sandisk SD Extreme Pro cards rated up to 90MB/s write speed, they are probably good maybe up for mRAW, but still not enough for RAW.... hoping the faster SD cards get developed some time in future as I really enjoy pure RAW mode ... and sometimes want to do a series ofshots formorethan 13 frames 😉

Do I need continous shooting mode daily for over 13 frames each time? no, not at all, but someone might and if you do then your only real option is 5DMIII camera (with similar full frame sensor) and a blazing fast CF card that could support infinite shots up to card's capacity.


Good news is that the SD cards are working great (as advertised) in 6D camera! 🙂


hope it helps.



The 6D supports UHS-1 cards.  The UHS-1 standard allows a theoretical bus speed of 312MB/sec.  I say "theoretical" because busses have overhead (usually one "large" file will transfer faster than lots of "small" files) but more importantly... nobody actually makes SD card technology that can transfer data that fast.  So really it's the physical speed of the card that becomes the barrier and not the speed of the bus.


I've seen UHS-1 cards with speeds rated up to about 100MB/sec (that's a rounded value).


The 5D III is different... it's CF slot is fast (CF card slots are generally always fast) but the SD card slot on the 5D III is _not_ a UHS-1 bus slot.  So it doesn't have the fast transfer speed.  If you _need_ that fast transfer speed on a 5D III then you'd want to make sure you've configured it to write to the CF card and buy an appropriately rated CF card that can keep up.


So far, I think only the 6D and the new 70D have UHS-1 SD slots.


If you have a 6D or 70D and you want that speed then you'd want to make sure that your SD cards are UHS-1 cards.  The symbol is a letter "U" with a "1" inside the "U".


Tim Campbell
5D III, 5D IV, 60Da

View solution in original post




From my Sandisk 45 MB/s 32 GB. You don´t get faster speed with a faster card.

Hello Guys,

I am a fresh and lucky owner of Canon 6D.

I have recently bought a brand new  "SanDisk Extreme 64GB SDXC 45MB/s 300X UHS-I Class 10 HD" to use with my Canon 6D and had a problem from the very first use. Has anyone ever had the error message "image cannot be read" ? Also images cannot be read on my computer... I have tried several image recovery tools but no luck. I have been advised to check whether if this SD card is compatible or not with this camera.. so far I could not find the relevant answer. I am really much after to be able to see this pictures taken if you know how and also figure out if what I should do about this card now.

Thanks a lot for who might be able to give me some guidance here !


P.S : I had used the same camera with smaller card from Panasonic and did not have any issue.


You did format the SD card with the camera?  Not your computer?  I would try another SD card and see if it works.  It should be fine.

Do the simple stuff first.

EOS 1DX and 1D Mk IV and less lenses then before!

Thanks for your reply. I did not try format the card since I would love to keep this images...

yes sorry another card works fine as mentioned in my first post...

"I did not try format the card since I would love to keep this images..."


I actually meant the first time you did format it.  But if another SD card works it doesn't look good for the one you are currently using, does it?

EOS 1DX and 1D Mk IV and less lenses then before!

I have a canon eos 6d and I went looking for a very fast card. Well I look into the scan disk pro and I found a 95 Mb card. I had purchased two cards for my Israel trip and it was well worth the money. I am going to purchase a few more because I love it.