Re: Run UBIFS on top of IDE mode NAND disk?

[Artem Bityutskiy <dedekind@infradead.org>]

On Wed, 2009-04-15 at 17:29 +0100, Jamie Lokier wrote:
> Artem Bityutskiy wrote:
> > Hi,
> > 
> > On Tue, 2009-04-14 at 23:10 -0700, Subodh Nijsure wrote: 
> > > I have board with 4GB NAND memory chip, it is configured to
> > > operate in IDE mode. And currently I am creating ext3 file-system
> > > on it.  This chip also have on-board controller that does
> > > wear-levelling, ECC so the quesitons are:
> > >  
> > > Can I (Should I) run UBIFS on of it and gain more of wear-levelling or its
> > > not worth it? 
> > 
> > Vs "Can I": if this is raw NAND, you just need an MTD driver for it.
> > Then you can use UBI/UBIFS on top of that.
> > 
> > Vs "Should I": you really should not ask questions like this. It is a
> > question of your design. Look at your NAND and how many erase cycles
> > each eraseblock survives. Then roughly calculate how many years or
> > months it should survive with ext3, which has fixed-position journal
> > and inode table and bitmap. Then decide whether you need WL or not.
> > Everything depends on your requirements.
> > 
> > Also, if this is raw NAND, then HW does not hide bad blocks for you,
> > right? How will you manage bad eraseblocks then, ext3 cannot do this.
> > It just panics in case of any I/O error.
> 
> But the on board controller does wear-levelling, he said.
> 
> I think the question is whether the on board controller's
> wear-levelling is good or not.  If it's low quality, UBI will do it
> better.  If the controller is good quality, there's no need for UBI on
> top of it.
> 
> I guess that two layers of good quality wear levelling just adds more
> wear, because they both copy data around.
> 
> If it can be used as raw NAND, and the chip really is a NAND with
> standard NAND properties, _and_ if it's possible to disable the
> controller's wear levelling and get direct NAND access, then at least
> you know that UBI provides a good quality wear levelling
> implementation, and you have access to some statistics too.

Right, he responded me in private (do not know why) and I
apologized for misunderstanding, and shared my thoughts.

-- 
Best regards,
Artem Bityutskiy (Битюцкий Артём)