NAND technology - ecc error

General Tech Technology & Software 2 years ago

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Posted on 16 Aug 2022, this text provides information on Technology & Software related to General Tech. Please note that while accuracy is prioritized, the data presented might not be entirely correct or up-to-date. This information is offered for general knowledge and informational purposes only, and should not be considered as a substitute for professional advice.

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manpreet Tuteehub forum best answer Best Answer 2 years ago

Nand technology has some issues, which I find it a bit difficult to understand. It is said in nand devices that manufacture guaranty that a page will have no more than X (4/8/16,etc according to nand device) failed bit.

  1. Is it that the manufacture can really guarantee that there shall never be more than this amount of failed bits is a single page ?
  2. Is it that the failed ecc happens just randomly, after some time ?
  3. Is it that re-program the failed ecc page, shall recover its flip bits to the correct value ?

Thank you, Ran

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manpreet 2 years ago
  1. No, it's all a game of probabilities. You just define a probability (e.g. 110141−10−14) that all pages fulfill that criterion, the manufacturer models the stochastic process that leads to errors and makes observations of that process, and you so get to a probability that indeed your criterion is fulfilled.
  2. There's different kind of errors. But yes, spontaneous bit flips can happen for thermal, particle / ionizing radiation, or current leakage reasons. Other errors are not spontaneous, but always immediately manifest. Note that a flipped bit doesn't mean the ECC must fail: Error checks are only safe against certain patterns of bit errors, and if multiple bits within a block (or page, or whatever you call it) fail, the ECC might not "notice" it. It's, again, a stochastic thing.
  3. Only if
    1. some recovery mechanism recovered the original data correctly; again, patterns, probability, and
    2. the reason the page failed because a bit flipped randomly. Of course, if a bit cell is simply stuck to a value, then there's nothing rewriting could solve.

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