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

[Miles Nordin <carton@Ivy.NET>]

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>>>>> "sn" == Subodh Nijsure <sunijsur@cisco.com> writes:

    sn> Hi, I have board with 4GB NAND memory chip

    sn> Can I (Should I) run UBIFS on of it and gain more of
    sn> wear-levelling or its not worth it?

I tried to do this with 16GB USB sticks.  There is currently some
limit in the mtd-utils around 2GB or 3GB.  I think you will have to
wait for the 64-bit ioctl patches to go in.

I would not expect bad-block remapping of ubifs layer to work at all
over an IDE device because IDE error handling is too goofy, and once a
bad block is showing through the proprietary wear-leveling layer, the
proprietary wear leveler may not be working sanely any more.  Probably
once the stick/board/whatever-it-is develops one bad block which shows
through the wear leveling, you will have to throw it out.

The reason I wanted to use it on my USB stick was not only for wear
leveling but because ubifs does checksums so I'll know if the cheapo
stick is corrupting my data silently.

And I think ubi has a scrub feature (which it claims is constantly
running in the background, thus much better than 'zpool scrub'.  on
ZFS they leave it as user's bother to initiate scrubs and thus user's
fault rather than the developers' if scrubs cut performance in half).

Also I hoped a log-structured filesystem would perform faster for
writing and have fewer of the weird problems described here:

 http://sqlite.org/atomiccommit.html

that plague overwrite filesystems like ext3/XFS/JFS/HFS+.  I wanted to
try it out.  

In general it looks to me like a really good idea to use the flash
filesystems over a layer of proprietary wear-leveling, but
supplimenting the proprietary wear leveling might not be the best
argument for doing it (because if the proprietary wear leveling is bad
in any but a few specific ways(like the old 16MB-chunk way), then you
are screwed anyway).  There are other good reasons for doing it
though.  Unfortunately there are scalability issues w.r.t. flash size,
and almost no one is doing this yet so it's likely to be clumsy.  I've
given up on it for a few years.

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