Interesting Podcast on Memory Cards

I listened to an interesting podcast by renowned wedding photographer David Ziser. He had data recovery expert Scott Tallyn on his podcast today to talk about flash cards, hard drives and data recovery. I found a couple of things that Scott said about flash cards interesting and thought I'd share them here.

1. The projected lifespan of a flash card is approximately 10 years. According to Scott, if you bought a card today, put it on a shelf for 10 years and then put it in your camera, there's a good chance that it won't work. (this was something he had read in an article recently and hadn't found out why this is the case yet)

2. A flash card is only good for 100,000 read/write cycles (each time you take a photo is a read/write cycle, each time you view the image on the camera is a read/write cycle, each image being transferred to your computer is a read/write cycle, etc.). So, if you don't chimp, each image has 2 read/write cycles. Scott recommends that a full time professional photographer should replace their cards every 2 years.

3. Flash cards are susceptible to damage from static electricity, so you shouldn't just keep them in your pockets, you should put them in a case.

4. He also said that the cards are more susceptible to being corrupted by filling them all the way up, so you should switch cards when you're down to about 5 images remaining.

If you're interested in the whole podcast, here's the link to David Ziser's Blog. He has the podcast player imbeded on the right side next to the section listing the questions he asked Scott Tallyn

 

Another point Scott Tallyn talked about that I forgot to mention was that many flash cards are made with two memory chips inside. Memory manufacturers do this because its cheaper to put two 4gb chips together to make an 8gb CF card. The problem is that if one of the two chips goes bad, the camera will write images to the card but they will be corrupt and you may not know it right away. Cards that are made with one chip are better because if the chip goes bad, the card doesn't work at all, preventing you from loosing images.

 

At least one detail isn't entirely right. Read/write cycle is a little misleading.

Reading shouldn't matter. You should be able to chimp to your heart's content without effecting the lifetime. I mean.. okay, it is still being used and there might be SOME stress caused by the access, but the real issue is the writing. Each time the memory is altered (written to) the physical structure is degraded a teeny tiny bit. Which is why the new generation of flash based mp3 players concern me. I guess the cycle life is still long enough as to not be a likely concern.

The recommended way to treat memory cards when you want to clear them off and use them again is just to format them, not delete everything. Theoretically formatting should result in more wear rather than less, deleting only touches the file allocation table entry for each file. I used to think formatting had other advantages, distributing the wear more evenly across the entire card, that sort of thing, but it looks like cards may have fairly sophisticated algorithms to try to prevent one cell from being worn faster than others, supposedly if you continuously write to the same file it'll actually spread the writes over the entire card, transparently. Also they're supposed to be able to detect the failure of a single cell and map it out, again without any user interaction required, so in theory even once you reach the cycle limit on one cell the others can continue onwards. I'm a little skeptical about that though, I'd want to see some testing that shows that it's reliable before I relied on it. I should also specify that the limits aren't hard limits, they're general estimates, individual failures probably vary, it's conceivable that the numbers might be lowball estimates and the reality may be better.
In any case the formatting may be as much about maintaining unfragmented cards as anything.

One other thing, the information I've run into from a quick google search appears to indicate that many flash memory devices might use a type of memory (MLC, multi level cell) that is only said to last 10,000 cycles. It looks like the cheapo 16gb card I got from Newegg is MLC. I'm still not too concerned, that's still an awful lot of cycles. I'll probably discard it from needing a faster UDMA card (maybe for the 5D mkII) long before it wears out from use. The alternative to MLC is SLC, single level cell. There I find the 100,000 cycle life estimate. And for higher end server hardware (I can't believe they're using solid state storage for servers, but apparently it's being used as an accelerator rather than as primary storage) I'm finding cycle lifetimes over a million cycles.