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FORUMS General Gear Talk Data Storage, Memory Cards & Backup 
Thread started 31 Aug 2017 (Thursday) 21:44
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CF vs SD Cards

 
lewie
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Post edited 7 months ago by lewie. (3 edits in all)
     
Aug 31, 2017 21:44 |  #1

Hi all, I've been away for a while.
I did some tests today with surprising results. All shot on my Canon 5D Mk III.
I used a Sandisk Extreme 60MB/s (a few years old now) to see how many full size RAW images would buffer before slowing. I got 15 images before I filled the buffer.
But, today I bought a Lexar Professional SD card with a speed of 150MB/s to try and get a faster transfer rate and only managed to get 9 before the buffer filled.
So how can this be? The Lexar (150MB/s) is way more than double the speed of the Sandisk (60MB/s) but only transfers half as many.
What is going on here? Any Ideas?
Cheers
lewie




  
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Nogo
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Aug 31, 2017 21:58 |  #2

Did you have a SD card in the slot when you tested the CF card. The write speed of a Canon 5d3 is slower to the SD card slot than it is to the CF slot. If you have a card in both slots, the CF card will not write at a speed faster than the camera can write to the SD card.


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CyberDyneSystems
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Aug 31, 2017 22:42 |  #3

This is consistent with the 5DIII and it's lack of support for the faster SD cards.

The 5DIII is in fact quite slow at writing to SD, so the faster cards can not be put to good use in that regard.


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lewie
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Aug 31, 2017 23:04 as a reply to  @ Nogo's post |  #4

The answer to that is no, I didn't have both cards in at the same time.




  
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lewie
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Aug 31, 2017 23:06 as a reply to  @ CyberDyneSystems's post |  #5

Okay and that makes sense to me. I've just ordered an 80D which only has one SD card slot so I'm hoping it's faster in that.




  
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CyberDyneSystems
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Aug 31, 2017 23:27 |  #6

It should be fine in the 80D


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Nogo
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Post edited 7 months ago by Nogo. (3 edits in all)
     
Aug 31, 2017 23:49 |  #7

I misread your cards. The Lexar 150 mb/s SD card is an UHS-II card. The SD slot in the 5D3 does not support the higher speeds of the II class card. I assumed the new card was the CF card because that is the card of that speed that the camera would support.

The fastest SD UHS-I card is around 95 mb/s. There is no write speed advantage to use a UHS-II card in the 5d3 or even the newer 80d or (7d Mark II, 5d Mark IV, etc.)


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davesrose
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Sep 01, 2017 01:01 |  #8

I have a Lexar UHS-II card rated at 150mb/s in my 7DII. The 7D2's maximum throughput for SD cards is 105mb/s. It works pretty well on the 7D2. There are just a few cameras from other brands that support the highest SD speeds (which has now surpassed maximum CF speeds). CF specs aren't going to get any faster because those formats are changing to CFast/XQD.


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Post edited 7 months ago by CyberDyneSystems. (2 edits in all)
     
Sep 01, 2017 01:06 |  #9

I am pretty sure the 5DIII won't even use the full speed of a UHS-1, it's not UHS-anything compliant.
Your going to get a little over 20MBs. That's it.


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lewie
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Sep 01, 2017 01:15 |  #10

Hey thanks everyone for throwing all the info into my thread.
I'm now far wiser thanks to you all :lol:




  
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davesrose
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Sep 01, 2017 01:16 as a reply to  @ CyberDyneSystems's post |  #11

I've got to admit, when I first got the 7D2, I slapped in the Lexar card. Then I set to continuous with body cap still on, but kept shutter pressed to hear the 10fps:-) I haven't used continuous much on my 5D3. The main action I take is bicycle racing, but I like taking that one shot that seems to be the height of action(and current DSLRs can have some pretty nice tracking ability).


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Sep 01, 2017 11:37 |  #12

Always best to check what the max write speed of your camera is before buying a memory card, although having a faster card and card reader that supports the speed does come in handy when transferring a large shoot. Canon seems to lag behind in supporting newer memory protocols and formats, sticking with what is fast enough to meet a target buffer size.


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eelnoraa
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Jan 05, 2018 18:18 |  #13

Nogo wrote in post #18441852 (external link)
Did you have a SD card in the slot when you tested the CF card. The write speed of a Canon 5d3 is slower to the SD card slot than it is to the CF slot. If you have a card in both slots, the CF card will not write at a speed faster than the camera can write to the SD card.

Having SD card in the slot and not writing to it won't affect CF card speed.


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eelnoraa
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Jan 05, 2018 18:22 |  #14

lewie wrote in post #18441848 (external link)
Hi all, I've been away for a while.
I did some tests today with surprising results. All shot on my Canon 5D Mk III.
I used a Sandisk Extreme 60MB/s (a few years old now) to see how many full size RAW images would buffer before slowing. I got 15 images before I filled the buffer.
But, today I bought a Lexar Professional SD card with a speed of 150MB/s to try and get a faster transfer rate and only managed to get 9 before the buffer filled.
So how can this be? The Lexar (150MB/s) is way more than double the speed of the Sandisk (60MB/s) but only transfers half as many.
What is going on here? Any Ideas?
Cheers
lewie

Like there mention, 5DIII's SD interface is limited to 25MB/s So any faster SD card won't help much. The only explaination I have for why Lexar UHS-II is slower than Sandisk UHS-I card is because Lexar card' backward compatibility mechanism is not very efficient. UHS-II card usually get optimized with UHS-II interface protocol. The optimization for UHS-I may not be executed properly. It is not uncommon


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eelnoraa
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Jan 05, 2018 18:25 as a reply to  @ davesrose's post |  #15

The limit for UHS-I interface is actually 104MB/s. The interface run at 208MHz, but there are only 4 IOs in SD that interface, so MB/s is half of that on the interface level. Beside actual data, commands, hand shakes also go through the same IOs, so actually speed for usable data is somewhere between 95-100MB/s. That is why all those Sandisk extreme and Lexar Pro UHS-I card has read speed of 95MB/s


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CF vs SD Cards
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