Re: Q: Filesystem choice..

[ebiederman@lnxi.com (Eric W. Biederman)]

David Woodhouse <dwmw2@infradead.org> writes:

> On Sun, 2004-01-25 at 14:53 -0700, Eric W. Biederman wrote:
> > The old papers on jffs2 would make it unacceptable as it reserves
> > 5 erase blocks. 
> 
> It's got slightly different heuristics now -- a proportion of total
> size, plus a proportion of total _blocks_. That was done primarily to
> deal with NAND flash, where we need _more_ blocks reserved, but it
> should also have helped with small NOR flashes. 
> 
> You blatantly don't _need_ to reserve five erase blocks to let you
> rewrite the contents of the remaining, erm, one erase block full of
> data. You can tune this; it's not a mount option but it's relatively
> simple to change in the code.

Has anyone gotten as far as a proof.  Or are there some informal
things that almost make up a proof, so I could get a feel?  Reserving
more than a single erase block is going to be hard to swallow for such
a small filesystem. 

> >  And I don't know if yaffs or yaffs2 is any better.
> 
> They're for NAND, not NOR flash.

I think I have heard about a port to NOR flash, but tuned
for NAND flash I would be really surprised if they were different.
 
> > In addition boot time is important so it would be ideal if I did not
> > to read every byte of the ROM chip to initialize the filesystem.
> 
> There have been efforts to improve JFFS2 performance in this respect. It
> still reads the _header_ from each node of the file system, but doesn't
> actually checksum every node any more.

That should help.  It bears trying to see how fast things are.

Eric