When you flick through the forums and boards, you can see a lots of posts from folks, that are about dropped frames in camera, even if the card is more than sufficient on paper or validated by the camera manufacturer.
This happens not only for SD cards, but also SSDs and practically every flash memory based medium. We all know, that the read and write numbers on the cards are usually measured under lab conditions, but you never get the same results in real world – so they are pretty theoretical. Same as advertised gas mileage of cars – nobody really expects to come even close, but since they are all off about the same amount, the numbers make them comparable. So yeah, business as usual, but why would a XYZ card, rated at – let’s say – 90MB/sec, work just fine for your neighbor, but if you buy the EXACTLY same card, and use it in the EXACTLY same camera, with the EXACTLY same firmware and settings drop frames?
Memory cards are incredible unreliable.
First you have to understand the way, how flash memory cards are made. They are not just flash chips, but they are much more complex engineered than you think.
Most of them are jammed with defects all over the place. That’s why there are dirt cheap (0.9 Nano-Dollars per bit). Memory cards are incredible unreliable The only reason why they work for you (except when they don’t work of course), they come with pretty sophisticated controller chips, that do all the error correction and bad block management under the hood. This is necessary, cause with every newer, faster, and cheaper fabrication process (that happens about every 12-15 months), the flash memory becomes even more unreliable. So the manufacturer has to come up with better and faster controllers, and a new set of EEC rules must be applied. So they really have to jump through burning hoops, to make the cards at least appear to be reliable.
Recycling and dirty little secrets under the hood
The quality of flash chips integrated into memory cards varies widely. It can be anything from pristine, spanking new material, to recycled chips with over 80% bad sectors. There is actually a reason, why cards, that have the same specs on paper, can have a way different price tag (and real world performance). Especially the cheaper cards are often made from second class, or even recycled material. Sometimes you can find a 32GB chip in a 16GB card. The missing 16GB are just bad blocks, that are mapped out by the controller chip. Since those controllers cost next to nothing, managed memory is much cheaper than raw flash chips with tightly defined specs. Just ct15 for the controller does the trick, to present the illusion of perfect, reliable data to the user.
Companies, who are known for their reliable media, usually have better material, and stricter and better quality control, but even they mix and match flash chips, yet sell the card with the same part number and name.
House of cards
So by using a controller, they can sell almost any bit of the wavers they made, without throwing anything away. That sounds like a win-win situation for everybody, and it usually is. When your USB thumb drive needs 4 more seconds to push the data over to your computer, you probably never know or even care. But when it comes to high demanding use, that pushes those cards on they edge, like recording raw video, the whole house of cards (pun intended) can fall down pretty quick. The controller usually does a good job, but it only can do so and o much, and that may be sometimes not enough, and you start dropping frames.
Yeah, I get it Frank. So what can I do?
Not much, since all the manufacturers work that way, and in 85% of all real world use, it’s not even a problem. But when you run into the last 15%, you can – at least – do some “damage control”
1. Return to sender
When you have problems with the speed of a card, return it as long as you can, and get one out of an other batch.
2. The right stuff
Personally I prefer Sandisk cards. There are other great brands out there, but Sandisk media never gave me any trouble, so I tend to stick with them.
3. Flush after you dump
Instead of just deleting the files on your card after dumping the footage to your computer, make sure you format the card before you go shooting again. Formating kind of resets the whole card (as far as possible) and gives you an almost brand new medium.
4. Don’t stuff it.
I never fill my cards up to the last bit. They tend to get slower and less reliable when almost full. I usually swap them, when filled to 80% – give or take.
5. Smart swapping
On a typical set, cards are much cheaper than anything that is going on in front of your camera. So if you just shot a very important or expensive scene, play it safe and swap your card.
6. Don’t cheap on your media
I don’t say this very often, but when it comes to media, you get what you pay for – except proprietary cards from certain camera manufacturers – there you have to pay more than what you get.
7. Think small
Buy more small media, instead of a big one. There is a trend to buy the biggest card available. The arguments I hear for that habit are hilarious IMHO. Like: “I miss shots, while swapping cards”, “I don’t want to carry so much cards with me”, “Swapping media slows me down”, and the best of all: “I can shoot a whole day on just one huge card, that’s so convenient”. No, that’s not convenient, that’s nuts.
If you ever have to pay (out of your own pocket) twice as much as you make in a month, for re-shooting a whole day, just because your “so convenient” huge card, decided to give up it’s ghost, than you know what I mean.