Re: Missing space on MMC2

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On Fri, Jun 06, 2008 at 05:38:40PM +0300, Eero Tamminen wrote:
> ext Marius Gedminas wrote:
> > That's what I do: reformat the card with the File Manager on the N810,
> > create a new swap file, then don't touch the card.  Later I will notice
> > that after a reboot my card is showing complete garbage:
> > http://mg.pov.lt/n810-fs-corruption.png
> > 
> > This has happened three or four times since I got my N810.
> > 
> > Initially I also had the problem with the FAT partition being a bit
> > larger than the device, but reformatting it with the file manager also
> > recreates the partition table, and it does that correctly.
> > 
> > Then I used the internal card to keep my valuable data.  Once I started
> > getting filesystem errors, rebooted and discovered that the partition
> > table was overwritten by the contents of a text file.  Since then I no
> > longer keep valuable data on the card.
> 
> Some reasons why FAT may corrupt:
> - User disconnects the USB cable without "safely unmount"
>    (similarly to re-inserting the memory card card, re-connecting
>    the cable doesn't help, device and desktop OSes forget the changes
>    once you disconnect the storage)

(1) I almost never use USB for transferring data.
(2) When I do, I always eject the card.
(3) You can't access the internal card over USB when you've got an
    active swap partition.

> - Device HW watchdog (not the SW one) rebooting the device

This may have happened, but how exactly can a HW watchdog reboot
scribble random data all over the partition table and/or root directory?
I'd understand if the FAT weren't completely updated and I'd get
cross-linked files or missing free space, but complete garbate in the
root dir?

> Are you sure neither of these have happened?

Watchdog resets have happened occasionally.  And I usually notice FS
corruption after one of those.

Still, that doesn't explain the other experiments I did earlier.  I
created a 1.7 GB partition (to be really really sure I'm not
accidentally trying to make the filesystem larger than the device),
formatted it as VFAT and created a single large empty file (dd
if=/dev/zero of=/media/mmc2/bigfile), and that caused vfat errors in
dmesg and, at least once, caused the *partition table* to get
overwritten with zeroes.  See this (short) thread:
http://lists.maemo.org/pipermail/maemo-users/2008-March/020492.html

> If you're sure, is an external card more reliable?

Yes.  I haven't ever seen FS corruption on the external card, and I
hadn't seen FS corruption on either of the two cards in my old N800.

(Although one SD card died *completely* while in the external slot of
the N800.  So completely that it spews USB errors and is invisible in
any SD reader I've tried.)

Marius Gedminas
-- 
Jim's Three Laws of Engineering:
  1. F = ma
  2. You can't solve a problem unless you know the answer
  3. You can't push a rope

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