Private with all due respect:
SD tech moved on quite a bit since the 1DS days. in fact 5d III to 5d IV = huge difference in SD card slot throughput. massive difference.
With 5D IV: SD slot is no longer being a serious limitation with 78 shots - 30 seconds of continuous shooting - vs 98 on CF.
therefore, writing to both card simultaneously is
a reasonable compromise, trade off in order to protect images. please read on..
with regard to what Mt. Spokane Photography just said and he is very close to the mark. Thank you. I would like to bring this into perspective if I may as I feel that this being an important subject:
I exaggerated, Its probably more like 150,000 write cycles before 10% of them fail, but I'd avoid low level formats until they are needed, such as before a long video
With
modern NAND memory -
Wear Leveling protection aside as low level format is full rewrite of every single byte of information - expectancy of the life is:
5000 to 10000 cycles (!!!!) ONLY !!!
it used to be up to 100,000 but with modern high density chip architecture and diminished quality due to cost saving race to the bottom, it is now roughly
5000.
Here is the message to naysayers:
the chances for the card to fail is dangerously high at 1:5000 for the brand new card. anyone who understand probabilities would not ever risk writing to a single card if what you shoot is valuable or worth a dime at least.
privatebydesign said:
On my 1DS MkIII's, which also had an SD and CF card slots, I only ever used the SD slot when I was shooting remotely so I could put medium jpegs on it to view remotely. Any other time I found it slowed the camera down too much, which has always been my biggest issue with the notion of a second card slot as a 'backup'. What use is it if it restricts speed and response?
The way Canon almost always implement dual slots (all but the 1DX) is not conducive to using them as a 'backup' strategy so I never do, even the 1DX MkII moved yet again to different capability slots!