Compact flash endurance check

I've experienced a lot of problems with the reliability of the CF cards.

IMO the biggest problem is not because of the wear, but because of the infant mortality of the unreliable cells. We ended up with the extensive read/write testing of every card and marking all suspicious clusters as bad. The number of the unreliable sectors may be huge: up to 2% of the total volume on some brands. After the bads are marked, the card doesn't cause any problems. Another observation: the bigger is the volume of the card, the less reliable it is.

From my experience, the CF cards generally support for the very limited subset of IDE instructions. You can rely only on the basic operations like read/write sectors; anything above that may or may not be supported.

Vladimir Vassilevsky DSP and Mixed Signal Design Consultant

Vladimir, Thank you for the reply.

I am curious about how do you find out suspicious sectors ?

Rgds, Vinod

A cluster which exhibits occasional read/write errors or can't be written or read from the very first attempt is suspicious.

Vladimir Vassilevsky DSP and Mixed Signal Design Consultant

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Careful - These devices do internal remapping for wear-leveling. The the sector you write is continually remapped to different physical flash. Depending on the mechanism used by your specific make and model of CF, doing a test as above is not so helpful (other than to flush CF cards that are going to fail very quickly).

See for example:

"Removable flash memory cards and USB flash drives have built-in controllers to perform wear-levelling and error correction so use of a specific flash file system does not add any benefit." / WPaperWearLevelv1.0.pdf

Hope that's helpful ! Best Regards, Dave

I am tired of hearing the unfounded speculations about remapping for wear leveling. Can you provide any *specific* information of if and how the remapping is implemented on the particular CF card?

If a cluster exibits occasional errors or the read/write operation has to be retried, it is likely that this cluster is going to fail. This is just the observation based on my experience with many different cards.

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Talks, stories and speculations.

BTW, in the newer designs, we use the bare NAND flash ICs rather then the cards. The reliability is much better.

Vladimir Vassilevsky DSP and Mixed Signal Design Consultant

Vladimir, I provided a link to Sandisk's implementation details above... Hope this helps, Best Regards, Dave

They seem to be a lot harder to source in large sizes and small quantities though.