How will an SD card fail?

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After a lot of use, how will an SD card fail?

This last week, I had an SD card that simply stopped working. And another SD card which I copied one file from, the file had some wrong characters on it.

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ESD?
I hope the SD-to-flash chip on-board has enough ESD suppression, or, there's room for ESD suppressors.

"Dare to be naïve." - Buckminster Fuller

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ganzziani wrote:
After a lot of use, how will an SD card fail?

This last week, I had an SD card that simply stopped working. And another SD card which I copied one file from, the file had some wrong characters on it.

Symptoms to me sound like software bugs, bad power, bad connector. SD cards' flash has a LOT of cycles on it before it goes flakey.

Assuming you flushed open files and closed the file system before ejecting the media, EVERY time.

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how do you use your SD card?

I do not know about SPI mode, but when using it on a PC using the on board controller to write to its memory space. the controller writes the data and then checks it. If the cell fails it will be marked bad and the data is written in another place. so this would mean that your SD card will become smaller and smaller until all is bad.

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It is actually possible to wear out your flash card, but you have to do thousands of writes to it though... But you said it had seen "a lot" of use?

I've had a compact flash card die on me for no apparent reason! Sometimes you just can't tell why they die... :(

- Brian

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My mom's SDcard failed mechanically - the plastic cover simply fell apart. This was after quite a lot of inserting/pulling out.

There are pointy haired bald people.
Time flies when you have a bad prescaler selected.

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ganzziani wrote:
After a lot of use, how will an SD card fail?
Always the buttered side down.

Stealing Proteus doesn't make you an engineer.

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Quote:

It is actually possible to wear out your flash card, but you have to do thousands of writes to it though... But you said it had seen "a lot" of use?

Surely that would only be true if you were repeatedly writing EVERY sector on the card. In normal use the controller on the card (nothing to do with the AVR or PC that might be interfacing to it) does wear-levelling and bad block remapping, just like the firmware/controller on a magnetic hard drive.

Forget the 100,000 kind of limit specified for "normal" flash. Because of the wear levelling you'd have to write to the card billions and billions of times to see flash failure effects. It's far more likely the gold plated contacts wear from insertion/removal (or the connecting pins that mate with those contacts lose their springiness) long before you can do logical damage to the flash array.

Cliff

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There are 2 basic types of flash used in SD cards. The "industrial" SD cards, which cost $$$, use single-bit flash. The normal consumer SD cards use multi-bit (or multi-level) flash.

Single-bit flash (where each flash cell represents 1 bit of data) is good for several thousand write-erase cycles. Multi-bit flash (where each flash cell represents more than 1 bit of data) is generally only good for a few hundred write-erase cycles.

SD cards contain a controller inside them, and they contain more flash blocks than what is "needed". The extra flash blocks are spares. As flash blocks fail the spares are swapped in by the controller - as a user this is transparent to you. At some point there are no more spare blocks remaining, and now when flash blocks die you see that - your card has problems or dies. With most SD cards being FAT16/32 formatted, it's the FAT file allocation table that's often the first to go, as it's rewritten so often. And of course if you lose the FAT, that's it for the data on the card.