OT: Problem reading 2GB SD card

[Lamar Owen]

On Tuesday 26 February 2008, Andrew Robinson wrote:
> Bingo! Tried an external card reader and I was able to extract all the
> images with no problem. Thanks for the help. I feel much better about my
> camera and SD cards.

The external reader must be SDHC compatible, then.  Most recent ones are.

> Now here's an interesting question. Before I erased the first card, I
> made a byte copy of it (`dd`). When I mount the byte copy with the
> loop-back device, it says files are there (as it did on the card).
> However, I cannot access the files. Anyone know of any tricks I can use
> to access the files? I'd guess I would have to repair the vfat file system.

How large is the image?  My guess would be that even if it is 2GB in size, the 
second GB contains the same data as the first GB, or contains random data.  
More likely, the image may only be 1GB in size.  This happened to me on a 
Sharp Zaurus SL-C1000 and the Cacko ROM with a RiData 2GB SD card.  As I put 
more than 1GB of data on the card, the earlier sections of data became 
corrupted with mixed data.

The issue is that some SD readers can't deal with capacities over 1GB; there 
is a standard for 2GB and larger cards called SDHC, but some older readers 
can't support it.  It is very much like how Windows 2000 SP3 and older 
Windows deal with hard drives over 137GB; addressing at the lowest levels of 
the disk hardware driver rolls over, and even though the OS sees the full 
disk size, the actual reads and writes to areas over the 137GB line actually 
are happening in the areas of the disk below 137GB.  Putting a 160GB drive 
(or larger) in a Win2k box without enabling LBA48 is a recipe for data 
corruption as the lower areas of the disk get overwritten when Windows tries 
to write above 137GB.  Been there, done that, lost data because of it.

WinXP prior to SP1 is in the same shape, incidentally.
-- 
Lamar Owen
www.pari.edu