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Our old SanDisk CompactFlash 256MB card died recently, during a photo session. My wife was taking photos with it - sometimes in humid environment -, then as she was browsing through the results on her laptop via a card reader, all of a sudden the next picture just came out a small rectangle in the middle of the screen. And then the next didn't come at all, and after that neither the laptop nor the camera could recognize the memory card anymore.

Luckily I found PhotoRec via a couple of posts here, and it saved our weekend - I could backup most of the (over 200) pictures from the card, but my wife says some of the earliest are missing. Then I tried to reformat the card, but it failed.

To me this looks like somehow the first sectors on the card got permanently damaged. All this makes me wonder, what could be the reason? As memory cards contain no moving parts, I always assumed they could live practically forever. Can anyone make a guess about this particular case, or give an explanation about the typical causes and ways of memory card failures?

Update: I forgot to mention that the card was not heavily used and it is approx. 8 years old, so I don't think it could have been written to more than maybe a couple of thousands of times.

"Humid environment" meant being in a sauna for a couple of minutes, not underwater :-)

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Sauna is a "condensing" environment which is bad for electronics generally, but I'd expect your camera to fail more quickly than the flash. However, water shorted connecting pins could definitely kill a flash card. For memory of that vintage, derate write cycles by about a factor of 10 to 1'000 to 10'000 +/- 25%. –  msw Jul 2 '10 at 14:00
    
@msw, I suspected short circuit myself to be a possible culprit, although the camera itself survived and is working fine. By derating cycles do you mean that the expected count of write cycles would be around 1'000 to 10'000 ? –  Péter Török Jul 2 '10 at 14:16
    
Correct, 1'000 to 10'000 write cycles as the fabrication process ten years ago wasn't as good and the controller logic was not nearly as smart. The stated write cycles are intentionally pessimistic, but like light bulbs - for example - even if the mean time between failure is 2000 hours, some bulbs will fail at 1000 hours and a tiny fraction at 10 hours. As ChrisF said: backups; I've never had flash fail me, but it can and probably will. –  msw Jul 2 '10 at 15:42
    
Just because the fault interests me, it is possible for a power pin to short to a data pin blowing the flash yet be "unnoticed" by the camera. I'm not betting on this hypothesis, but there 'tis. –  msw Jul 2 '10 at 15:45
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up vote 4 down vote accepted

Memory Cards (or SSDs) have something called "write endurance" which limits the number of times you can write to them. A search for this term or "write limit" will bring up a lot of pages which will give you a lot more detail, but basically:

The number of write cycles to any block of flash is limited - and once you've used up your quota for that block - that's it! The disk can become unreliable.

Source

It's usually quite a large number, but I would assume that it could be affected by things like temperature, humidity, shocks etc.

I would work on the assumption that the drive could fail at any time. Keep it backed up and always carry a spare.

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Flash has a limited number of write-cycles, measured on the order of 10000 to 100'000 writes. Some cards have controller logic to mark and avoid segments that have gone bad, but flash will ultimately fail. Environment likely had little to do with it (unless "humid" meant "underwater" or "with heavy condensation dripping off everything").

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