David Young  asked;

>> but the decision was made weighing "the rootfs is
>> seldom written beyond configuration mods by administrators."  Software ECC
>> is always calc'ed and verified, block write is counted and recorded inside
>> NAND spare fields.
>
> How do you handle the bad blocks that develop as the device "wears" ?

The answer is "by manual intervention," just like good-old-days Winchester
style hard disk drive bad sector management practice.  I wrote a cmdline
tool to manage bad block list and relocate block contents.  In principle we
neglect the whole NAND woe/buzz to happen due to the above mentioned
rational.  "this tools may cause hazardous results to hurt you, trained service
personel only, or don't use this."

If I have chose MMC/SD/CF media to go, I would build vnd on a large file
on the FAT filesys and forget how good/bad to gauge badblock and
wear-leveling schemes inside.

Toru Nishimura/ALKYL Technology