Re: [Yaffs] Products shipping YAFFS ??

Hello Charles,

On 3/4/07, Charles Manning <manningc2@actrix.gen.nz> wrote:
> > a) YAFFS2 is not in the mainline, thus gaining less testing/support
> > from the open-source community
> This is possibly true, but I don't think that it ncessarily follows. Just
> because stuff is in the mainline does not mean it is well tested. I have
> found more than one driver in the mainline that got broken due to a kernel
> change impacting on a driver.

Yes, that's certainly true. Still if yaffs2 were in mainline, more
people would have been using/testing it. That actually was my point.

> > d) YAFFS2 is likely to be slower with bitbanging NAND due to hard OOB usage
> Can you explain that a bit more. I don't understand what point you are trying
> to make.

YAFFS2 uses OOB area more intensively than JFFS2, so in order to
read/write things it issues more NAND commands generally, which turns
to be a performance drop for GPIO/bitbanging NAND controller
emulation.

> > f) YAFFS doesn't implement any wear levelling AFAIK which is a minus.
<snip>
> If is true that YAFFS does not do any explicit wear levelling. Instead, a
> degree of wear levelling is a side-effect of how free blocks are managed.
> Although the code and motivation is entirely different, the result is similar
> to how the SmartMedia/SD free is managed but the pool is typically far larger
> for YAFFS meaning that the wear levelling is far better.
>
> To explain that last statement a bit: In a FATfs on SmartMedia/SD, typically
> 1000 out of 1024 blocks are formatted and in use and the free pool is only 24
> blocks (reduced by the number of bad blocks) this makes the pool relatively
> small meaning that the averaging effect is only scattered over a few blocks
> at a time. In other words: a formatted block is "in use" whether it holds
> data or not. In YAFFS, blocks that do not contain useful data are unused and
> in the free pool. This means that the free pool is typically far bigger and
> the averaging effect is better.

Thanks for the explanation, I must admit myself being wrong here.

Vitaly