[maemo-users] Missing space on MMC2

From: Marius Gedminas marius at pov.lt
Date: Fri Jun 6 18:58:14 EEST 2008
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:

> 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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