What kind of error is this?

I was recording both RAW and JPG images to my SD card at the same time when shooting this evening. Two times in a row this error happened...both the RAW and JPG files look like this. I immediately switched to record to my CF card and had no issues. Does this look like an SD card problem? Thanks in advance for any input.

Some kind of data transfer issue.

Sounds like they looked like that in the camera and when you downloaded them to your computer and converted them?

Yes, they appeared this way in-camera on the LCD, and when the files were displayed on my computer. When you say "data transfer error," is that a card problem or a camera problem?

second one looks similar to a "normal" corrupt file type, but the first one is more serious - you've effectively saved half of two shots on the one file which is rare.
Basicly appears to be a buffering issue.

I'm guessing a main board issue on the camera, is it under warranty? if so, get it off to Canon pronto with copies of the corrupt files for them to look at.

Can you reproduce it with the same SD card? How about with a different SD card?

The fact that you have no issue with CF and only problem with SD sounds like a SD card issue. SD interface is serial and quite robust. It is unlikely to have transfer issue from SD card. CF is more susceptible to transfer error. However, the flash memory in SD is most of the time lower quality than CF. What is SD card is this?

joseph - thanks for the input. Unfortunately, the camera is almost five years old; I got it right when the 5D MK III was launched. It has been a wonderful tool and should still have plenty of life left in it. Hopefully it isn't a board issue, but I appreciate your insight and will keep a close eye on things.

Data transfer relies on the sending and receiving device both operating and communicating almost perfectly. There are checks as part of the process to make sure things are going well and correct any errors, but when those fail, there is corruption.

I'm no genius, but I don't think anyone can narrow down where the failure happened by looking at a corrupt image. IMO, the card is the most likely culprit. (Edit: but that is just because I believe they are the weakest link) I have a zero tolerance policy with cards that act weird ... one chance, after the first weirdness it never gets used in my camera again.

I would set it aside and see if the problem happens under the same circumstances with another card.

eelnoraa - thanks for the info. A photo of the card is attached. I haven't been able to replicate the problem with this card or any other, despite having all the settings the same.

The other variable which I guess I have to consider is a possible problem with the additional circuitry associated with two connected strobes. The camera was being used in an underwater housing, with two strobes connected via a TTL sync cord, and the housing has the circuitry in it to manage the strobes. It's all made by Ikelite, specifically for the 5D MKIII, and it has given me years of great service without trouble.

So far what I have learned is that I need to use this card only for single-shot slow work, like landscape shots, and monitor it closely for errors. And be sure to be recording to both cards at the same time to make sure I don't lose a shot. And when using the whole rig underwater, use a different faster SD card, and watch for a repeat of the issue.

Is that white and red part a second label on top of the gold label?

None of my sandisk sd cards have that. They are all just one label.

Fake cards are all over eBay and Amazon.

No, it is all one label. I don't recall where I purchased the card, but I usually only buy from reputable sellers (B&H, Adorama, etc.). If I bought it from Amazon, it wouldn't have been a third-party purchase; I would have bought it straight from Amazon. I know the difference between their inventory vs. third party pass-through. And as far as I can recall, all the cards I have bought over the years have come in full manufacturer packaging.

On the back there is a printed serial number; I'll do a web search to see if there is a way to verify that a card isn't a fake using the serial number.

Extreme Plus has a lifetime warranty. I would give Sandisk a call. They are very good about checking to see if fake and if real offering replacements.

Ed, are the shot numbers consecutive? in that is the sequence of numbers normal for both the shots that show problems and the ones either side?

Not sure I totally follow your question, but the two problem shots were consecutive. I recorded two raw files and two jpg files, all showing the same problem. Of course it was just two unique file numbers with different file types.

just trying to work out if good image 1, is followed by bad image 3 (thereby missing #2 that 1/2 overwrote #3 if you catch my drift)
I vaguely remember reading of someone that had the same issue, not sure what body it was though.

Did a quick google of 5D3 image corruptions & came across a dpreview thread with similar split-image corruptions (Linky) third example looks quite like yours.
sadly the poster didn't seem to come back with why it happened or what was done to fix it.
Is your firmware the most recent version? might be worth trying an update if it isn't current.

Big Ed, do you regularly format your cards in camera?

Ever do a low level format?