Record to both CF AND SD cards on 5Dm3

[mjroddy]

Can we record to both the CF and the SD cards at the same time on our 5D3 cameras?
I thought we could, and I set up the camera's menu to:
Record Func. = Rec to multiple
Playback = [2]
But when I record a clip, it ONLY seems to record to where I have the "Playback" pointed.
Is that Record to Multiple ONLY for still images?

[ebiggs1]

"One practice I was told to use is to (for CF cards) format the card first in your computer, then again in your camera just before use."

I doubt seriously that does any good.

You have something like a "table of contents" that tells the camera if each sector on the drive is being used.

Formatting it changes the table of contents so each entry is set to available. 

It no longer acts on any other portion of the card.

I would also not recommend formatting a CF card with your computer. Just use the camera.

[mjroddy]

You have EXACTLY the same thinking I had. But the above advice came directly from the tech support guy. 

My problem is that I had REALLY fragmented frames and hard-core dropouts.

In other words, some frames were split in two, where the top half showed a frame from some random place on the disk, and the bottom of the frame was right with the flow of the video file.

Other times, I had what looked like an old-style video dropout, where the video just became a garbled mess for about 15 frames!  Oh so odd.

The tech explained that the camera only writes a new table and that means that all files should get overwritten.  Problem is (he said) (and was "confirmed" on other forums/sites) that the remenent files can "bleed through" (don't ask me how, I don't know, I only do eyes), which is producing the very offending problems I was experiencing.  And indeed, the problems mainly existed the more the cards got used.

One guy on one of the forums says that he "tests" all his cards by setting them up in front of a TV and letting the cards fill up.  Then he'll wipe them using the method I described, and do that no less than 3 times.  If the speeds still hold and he has no dropouts, he puts the cards into his work flow. 
My problem with that is, who's going to watch 32-64GB of recorded TV looking for the odd dropout!  Yikes!  (But it has to be done, I suppose.)

Unfortunately, I have been deep in editing and haven't had the chance to really work with the cards much since my original problems.

[ebiggs1]

OK, I am pretty sure they are talking low-level formatting not quick format? This is different.

The manual:

•Do low-level formatting if the card’s recording or reading speed seems slow. 
•Since low-level formatting will erase all recordable sectors in the SD card, the formatting will take longer than normal formatting. 
•You can stop the low-level formatting by selecting [Cancel]. Even in this case, normal formatting will have been completed and you can use the SD card as usual.

IMPORTANT

When the card is formatted or data is erased, only the file management information is changed. The actual data is not completely erased. Be aware of this when selling or discarding the card. When discarding the card, execute low-level formatting or destroy the card physically to prevent the data from being leaked.

This low-level format takes longer as it writes 0 to all sectors of the card. You must remember a CF card is not like a hard drive where you can have layers. A CF card is either a 0 or a 1. Once that is changed all data previously on it is lost.

[mjroddy]

I don't know if it's right or not, but my practice is this:

CF Cards - LowLevel Format in computer, then Format again in-camera

SD Cards - LowLevel Format in-camera (only)

Again, I haven't really tested my CF cards since they burned me.  I need to do that despirately, so I can confirm this works to a professional standard.