Re: [RFC] read-only filesystem support for NAND flash devices

Vitaly Wool
2006-05-10T11:20:34Z

Josh Boyer wrote:
>> As a filesystem is read-only, wear-out can't occur during the normal
>> use, only on root filesystem upgrade. Therefore writing it using a tool
>> like nandwrite that bypasses bad blocks seems to be enough, and the only
>> thing needed is either an in-MTD layer that makes a partition look as if
>> there's no babd blocks, or similar means within a filesystem.
> Not quite the case. You need bad block skipping, yes. But NAND can
> get bit flips in good blocks still. How do you deal with that? You
> can't leave the block in that state forever because it will continue
> to get bit flips and then your data will be unusable.
Yep, I know about the issue. The recommended way to go here AFAIK is to
mark the block as bad and copy its contents to a free one.
However, this will make mapping a lot more complicated so I'd like to go
another way, i. e. erasing and rewriting this very block, and if it
wears out, cache the data read from it and schedule moving the data
forward within the partition in a background. Does that make sense?

Vitaly