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

Josh Boyer
2006-05-10T17:21:02Z

On 5/10/06, Atsushi Nemoto <anemo@mba.ocn.ne.jp> wrote:
> On Wed, 10 May 2006 06:00:57 -0500, "Josh Boyer" <jwboyer@gmail.com> wrote:
> > 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.
>
> If I mounted a JFFS2 filesystem on NAND and _never_ write anything (or
> mounted read-only), does current MTD/NAND/JFFS2 layer handle those bit
> flips? I've thought JFFS2 only reassign blocks on writing, so JFFS2
> also suffer those "bit flips on read" problem, is it right?

If you truly never write anything, then yes it probably suffers from
the same problem. In a typical JFFS2 setup where writes do occur, the
theory is that garbage collection will eventually reclaim that block.
Whether that actually happens or not is largely determined on a per
use case basis.

josh