A few nano questions

Rubén Berenguel ruben at mostlymaths.net
Sat Jun 5 05:22:43 EDT 2010


I read two Toshiba presentations on NAND+ubifs... it looks a little
scary, yes :) But, I'm not sure if SD cards ahve the same wear off
effect. I remember from somewhere that the average NAND life is
10000-20000 rewrite cycles, and ubifs tries to even that by not using
the same space again, but spreading over all the disk.

I wonder what will happen to the nano when the NAND starts to fail...
I guess, if there is enough working room in it to write the boot
system (as reading does not damage NAND disks), it will always be able
to boot from the SD, will it? Usually the worst part of a portable
computer is the hard disk (maybe also the motherboard), when the hard
disk fails the laptop can go to waste. I wonder if we will still be
using our nanos to show our children (or grandchildren, depends on
your age) what Linux was like, 20 years from now.

Ruben

On Sat, Jun 5, 2010 at 11:16, Wolfgang Spraul <wolfgang at sharism.cc> wrote:
> Ruben,
>
>> Can I use any other USB-mini USB cable to connect my computer with the Nano?
>
> Yes sure, you can. We have seen some really bad USB cables that caused
> problems, see the notes here
> http://en.qi-hardware.com/wiki/Ben_NanoNote_Production_Process#Reflashing
> But these USB cables would cause problems anyway, they are just bad. Maybe
> one indicator for a bad cable is if it is unusually thin.
>
> But in general, if it's a good USB cable and meets USB standards, any cable
> will work.
>
>> What do the UBIFS messages about PEB block scrubbed, moved to... mean?
>> (I mean, I know it means a CRC error and that the data has been moved,
>> but what does it mean for the integrity of the disk and operating
>> system? How often I am supposed to see them?)
>
> That's a long story, I do believe NAND and MLC support in general is improving
> in the Linux kernel and ubifs, but that's just my guess, maybe wishful thinking.
> It's pretty safe to say that NAND is a tricky technology, which needs a lot
> of 'smart' software to make appear as a solid and stable storage medium :-)
> The more you know about NAND, SLC, MLC or all the new variants, the less you
> will want to use it for any valuable data.
> But if that still doesn't scare you, google for ubifs, slc, mlc - there are
> some good articles.
> http://www.linux-mtd.infradead.org/faq/ubifs.html#L_ubifs_mlc
> Some people think hiding this from Linux in the form of a microSD card is the
> way to go, I'm not one of them. That just means there is a small additional
> IC next to the NAND chip, which of course is proprietary, and has the
> exact same wear-leveling and ECC handling software running that we may or
> may not be able to get to work in Linux.
>
> I was a bit worried when we started selling Ben NanoNote that our NAND and
> ECC handling would not be robust enough, but for my own Ben I never had a
> serious problem, and I haven't heard anything from others.
> Maybe on the next run in the factory, we can try to gather good statistics
> from a larger set. That's something we wanted to do for a long time, but when
> the day comes there are always other things that are more important.
>
> So I appreciate your feedback, let's keep an eye on NAND stability, actually
> if the ubifs developers don't have enough MLC NAND devices to play with maybe
> we should point them to the NanoNote... :-)
>
> Wolfgang
>
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