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kmeisthaxtoday at 4:02 PM1 replyview on HN

NAND[0] has a fun thing called "read disturbance" where repeated reads from disk will eventually flip 0s to 1s. You have to erase and rewrite the block before the bits flip[1], or you lose the data, but doing so is the same amount of wear as a write.

[0] I heard this being an issue with TLC, I don't know if it also applied to MLC or SLC.

[1] I suspect in practice they use an error correction code and rewrite blocks that read with corrected errors.


Replies

wtallistoday at 4:14 PM

It's kinda irresponsible to talk about read disturbance without clarifying that it takes an extremely large number of reads to cause a read disturb error, and it can be corrected by a single rewrite of the data. Read disturb errors are something SSD engineers need to account for, but from an end user perspective it's a smaller problem by multiple orders of magnitude than write endurance, which is already rarely a real problem in practice.