Is One Card Slot Enough? How to Prevent Corruption For Any Card-based Media.

SD Card Close-up

It was just a year ago when I wrote my guide “4 Tips On How To Avoid Getting SD Cards Corrupted”. I had no idea how relevant it would be now, seeing the paranoia and teeth-gnashing photography geeks are going through at the moment. Yes, both Canon’s and Nikon’s first foray into full-frame mirrorless introduced cameras that only feature one card slot. And if you have read the guide linked above, you would think that it actually does not matter. And you are right! Consider this follow-up article a successor to my original article, with more information and clearer explanations.

A little history

We started with wet plates in the early days of photography. So if something bad happened to that wet plate, the image was lost. Then we had film photography, and if something bad happened to that roll of film, images get lost. Then we moved to digital photography and card-based storage media. If something bad happens to that card, images get lost. Card-based storage media was in its infancy and could be unreliable. It was not until much, much later that we started getting 2 card slots in selected cameras.

But things have changed as technology progressed. As long as you are using a card from a trusted vendor and know how to manage your card-based storage media intelligently, the possibility of file corruption is nil. Consider the following fact: An indescribable order of magnitude more people than photographers routinely save and delete apps, photos, video clips, music, full-length movies and drama episodes to the single-SD card in their mobile phones and never have a file corruption problem.

Photographers, actually it’s your fault

So why is it that photographers seem to have such bad luck with their card-based storage media? One reason is historical fear. It is like how some old folks I know of still insist on turning off every electrical switch in their house before they leave their home (But they could tolerate letting the refrigerator run.) in case they blow up and start a fire. Some photographers had some expensive accident in the historical past and never got over their phobia. Another reason is lack of education about card-based storage media while trying to employ what they believe are smart ways to improve redundancy – often causing damage themselves.

Your normal mobile phone user do the right thing. They just left the same SD card in the phone, forever. Photographers with their “smart redundancy plans” end up with corrupted files, while the happily ignorant casual mobile phone user never has a problem.

The dual-card slot redundancy proposal is actually a failure

Dual-card slots are useful when you want more storage for a shoot so your media can overflow from the first card into the second card, without you having to remove them. They are also useful for saving RAW on one card and JPEGs to the other, so you can quickly deliver results using the card with JPEGs while keeping the RAW files for future processing if necessary.

But as a kind of RAID-1 redundancy solution to keep a duplicate of all your media as a back-up, it is a failure. It might have been useful during the early days of card-based storage media when the technology was not mature enough, but it just does not make sense today. Anyone working in IT knows The RAID-1 concept is a very limited solution, because we are still stuck with a single point of failure. But this isn’t the biggest failure of this proposal.

The biggest failure of the dual-card redundancy proposal is that it offers no protection for that media which is most expensive to lose – video. Which basically already ends the discussion already. If a solution can’t protect the most expensive thing that can be lost – it’s a useless and meaningless solution.

By the way, no camera record high quality video to two separate storage media. Even an Arri does not do it. But that is OK, because the people who work with an Arri – the same people who stand to lose millions of dollars of shooting expenses if they lost a day’s video to data corruption – understands more about data management then “self-declared professional photographers” screaming for dual-card slots for redundancy.

If we think deeper about this, Phase One cameras only write to a single storage media. As do Leica rangefinders. As do commercial drones capturing footage. As do the Arris and the Reds creating very expensive visual content for cinema and television.

Photographers corrupt their own card-based storage media

Let me go through the ways a photographer cause corruption to their own card-based storage media.

1. Removing a card prematurely
Some photographers implement some “smart redundancy” plan where they regularly swap out cards during an assignment for constant backups or similar. Obviously, pulling out a card when the camera is still writing to it is a very bad idea. These supposedly “smart” redundancy plans just increased the risk of memory corruption – and it’s actually the “smart photographers” doing it to themselves.

2. Incessant removal and insertion of card-based storage media
Constantly removing and inserting card-based storage media between cameras and card-readers is not a good idea. You could break a connection pin. So, try not to do it. Cameras include those high-speed USB connectors for a reason! And yes, this is again anathema to those “smart redundancy plans” which are actually not very smart after all.

3. Why do you trust the card reader?
You know that card reader you are incessantly inserting and removing your cards into? Do you know who made it? Do you know who made the internal electronic parts? Do you know if cheap parts were used? It is ironic that people who are so hung up about protecting their data are so eager to shove their precious cards into hardware that they probably don’t actually trust.

4. Why do you trust the card reader’s firmware?
All card readers have firmware to help load the file system on the card. Again, why should you trust the firmware on the card reader? Do you know who developed the firmware? Do you have any guarantee how reliable it is? If you can’t be sure, then why are you so eager to use them?

5. The card also has its own firmware
It may come as a surprise to many, but SD cards have a teeny tiny micro processor embedded into it, running its own firmware to manage the flash memory, including bad areas. If you consider this with points (3) and (4) mentioned above, from the perspective of data integrity management it becomes very uncomfortable to be regularly swapping cards among different devices with different builds and possibly different versions of file-managing firmware.

I have seen perfectly fine SD cards immediately raise a file system error upon removal and plugging into a card reader. Then it is no longer fine upon re-inserting into the camera.

6. Using cheap cards from an unproven brand
For some things, you do get what you paid for. Some companies can build very attractively priced cards. But think carefully before investing.

7. Not formatting regularly
It is a good idea to re-format the file system regularly. It also helps the card’s firmware to re-organise data around bad sectors and reduces fragmentation.

8. Not retiring a card
Card-based media do have a mean-time-to-failure. Depending on your usage frequency, it is good to retire some old cards after a few years. Anyway, new cards with faster speeds and larger storage will be available, so this can be considered to be a normal part of technology progress.

How to prevent card-based media corruption

Just looking through the points we raised in the preceding section, we arrive at the following recommendations:

– Leave the card in the camera. That high-speed USB connector on your camera is there for a reason. Use it to copy files. Minimise removing cards from the camera.
– Be very wary of card readers unless you really trust the brand. In fact, I avoid them altogether. If I have several cards to process, I will cycle through them using the camera and use USB to copy the data out.
– Buy your cards from reputable brands.
– Format your cards regularly.
– Retire your cards at a stipulated schedule. In fact, I know some photographers just pass the card to the client as part of the cost of their business.

You can get to zero media corruption with these recommendations. I did. Stop worrying about stuff that isn’t worth worrying about and keep shooting.


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