red dots on NAND map when usb updating
wmb at laptop.org
Wed Oct 8 17:36:15 EDT 2008
The red dots in the NAND display ("scan-nand" or "copy-nand" or its
equivalent) are bad NAND erase blocks.
An erase block is a 128K chunk that has to be erased as a unit. The
erasure process gradually wears out the block (charge accumulates in the
dielectric and shifts the thresholds to the point where that section of
silicon is forevermore unusable).
A few bad erase blocks per device from the factory is normal. Over
time, so more will accumulate, but hopefully not too quickly, if the
wear-leveling software is doing its job.
The minimum writeable unit is a 2K page, so each erase block has 64
pages. Actually, you can write chunks as small as 512 bytes, but the
hardware ECC operates over 2K chunks, so it's difficult to use sub-page
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