microSD && ext3 file system

[Dr. H. Nikolaus Schaller]

Am 03.04.2012 um 19:06 schrieb Ed Kapitein:

> On 04/02/2012 08:49 PM, Matthias Apitz wrote:
>> El día Monday, April 02, 2012 a las 08:32:51PM +0200, Jiří Pinkava escribió:
>> 
>>> Hi,
>>> 
>>> after umout is the filesystem broken? I have experience where are writen 
>>> some pseudorandom data, which overiwrite even forst sector (after 
>>> restart disk partition are not show, SD card is "unformated").
>>> 
>>> Is this you case?
>> Hi,
>> 
>> Not exactly. It seems that through writing files to the ext3 file system
>> it gets broken; and after this "fdisk -l" does not show the partition
>> anymore;
>> 
>> btw: when I format this with mkfs.vfat, all is fine; but the space is
>> only 1GB while the partition is around 4GB:
>> 
>> root at om-gta02 ~ # fdisk -l /dev/mmcblk0  
>> 
>> Disk /dev/mmcblk0: 3953 MB, 3953131520 bytes
>> 4 heads, 16 sectors/track, 120640 cylinders
>> Units = cylinders of 64 * 512 = 32768 bytes
>> Sector size (logical/physical): 512 bytes / 512 bytes
>> Disk identifier: 0x0aecb0ac
>> 
>>        Device Boot      Start         End      Blocks   Id  System
>> /dev/mmcblk0p1               1      120640     3860472   83  Linux
>> root at om-gta02 ~ # df -kh /dev/mmcblk0p1
>> Filesystem                Size      Used Available Use% Mounted on
>> /dev/mmcblk0p1         1022.0M    394.0M    627.9M  39% /media/card
>> 
>> Why is this?
>> 
>> 	matthias
>> 
> Hi Matthias,
> 
> A while ago i read this article on [1].
> Perhaps this will help you to solve your problem.
> ( i have a hard time finding a working uSD card too )
> Is your card on the supported card list [2] ?

I recently came across a different possibility: a broken
SD card reader. It may work well for SD cards up to 2 GB
but fail for 8 GB cards.

It took me approx. 3 days of intensive cross-testing to
find out that the microSD cards were all ok. And only the
brand new SDXC compatible USB card reader (even originally
branded by the SD card manufacturer!) was broken.

The symptom was that it did read 100% ok. But write access did fail
in approx. 1 out of 10k writes. So it damaged sectors within
files - without changing the file tree. So fsck did not
find anything. Only rarely and spurious.

So please try a badblocks [3] on the system where you create
the card.

If it shows bad blocks and a second run shows them in a different
location, your reader is broken and not the SD card...

> Kind regards,
> Ed
> 
> 
> 
> [1] https://lwn.net/Articles/428584/
> [2] http://wiki.openmoko.org/wiki/Supported_microSD_cards
> 
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[3]: http://linux.die.net/man/8/badblocks