SD Card only fills halfway

[Lennart Sorensen]

On Fri, Feb 11, 2005 at 08:46:31AM -0500, Andy Jack wrote:
> I experienced somewhat similar behaviour with a CF card - it would
> regularly lock up my (cheapo) MP3 player mysteriously.  Turned out there
> was a bad block or two that was fixed with the following command:
> 
> mkdosfs -F 32 -c /dev/whatever

Using fat32 automatically changes the root dir into a normal dir rather
than a special dir, and now the dir entry limit disappears for the root
dir solving all those problems.

> "-c" checks for bad blocks.  "-F 32" specifies FAT32.  mkdosfs is, as
> you might guess, a FAT formatter for *nix.  IIRC, formatting under
> WinXP couldn't rectify the problem.
> 
> The man page for mkdosfs states that the default number of root entries
> is 112 or 224 for floppies and 512 for hard disks (although that could
> be mkdosfs-specific).  mkdosfs does have an option to change this
> number.

Yes that was the limit for FAT12 and FAT16.

> Possibly, there's a little bit in the middle that's dead?  If, by
> reformatting with bad block checking, you cause the new FAT table to
> ignore this part, you might be able to recover most of the space.

Maybe something like dd to read and write the whole device and see if
any blocs fail, or the badblocks util (although it might not entirely
apply to flash memory cards).

Lennart Sorensen
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