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Re: Re: RE : JFFS2 for NAND flash file system


* Paul MAILLET <paulmaillet37@gmail.com> wrote:
> For me it is clear that the FS has nothing to do with all the NAND
> drawbacks, it's the job of the NAND support layer, isn't it?
> PS : Is the Linux mtd layer (or a part of it) the equivalent of the
> eCos NAND support?

This would be correct from a traditional strict-abstractions worldview.
I don't know the full history, but for whatever reason this did not happen
in Linux when MTD parts came along.

The crux of the issue is how you view the NAND drawbacks: are they
issues to be worked around so you can reuse your existing filesystem,
or are they reminders that you are dealing with fundamentally different
technology which does not allow you to make the same assumptions you
were used to?

Both eCos NAND layers are similar in scope to the Linux mtd layer.
They both targetted YAFFS, so it was clear from the outset that they were
going to do a similar job to MTD. (Of course, they were both designed
specifically for eCos so are not identical to mtd.)

It is interesting to note that manufacturers of USB memory sticks - which
often contain NAND - do deal with just these issues in order to allow
their devices to be used with arbitrary filesystems (usually FAT). There
is an argument to be made that Linux and eCos should consider building
in such a translation layer, but I seem to recall that there were patent
issues, possibly arising from the USB memory stick manufacturers. Also,
I suspect there could be an overall efficiency penalty (as compared with
a flash-aware filesystem) if a NAND interface was to hide the drawbacks.


Ross

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