NAND flash misery


Guess how many bad blocks are typical for NAND flash of several GB capacity? As many as 2 percent! There could be the whole areas of hundreds of megabytes of the contiguous bad cells, as well as the random scatter.

It is possible to do the extensive read/write test to find the most of the unreliable blocks; but it takes many hours.

I didn't encounter this problem until we started to use the high capacity CF cards. The bad blocks were very rare for the cards of 1GB and below. Since the flash iself is hidden behind the IDE interface and a compatible file system, and the read/write performance is critical, it is generally impossible to apply an error correction scheme.

I was under impression that flash is more reliable then HDD; now I see that it is not so. Do you know how reliable are the IDE flash drives?


Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com
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