fun with SD cards

[Mitch Bradley]

The mount time for a 4G JFFS2 volume will be pretty long.  Another 
problem is that you will use up a lot of kernel memory for JFFS2 
internal data structures with a volume that size, assuming that you put 
a lot of data on it.  We have pushed JFFS2 well past its design center 
with the 512 MiB FLASH.  It was really designed for FLASH sizes in the 
32-64 MiB range.

I will probably get piled-on for saying this, but in my experience, 
plain FAT filesystems work well for removable media.  FAT was originally 
designed for removable media (floppy disks), which is not the case for 
ext2.  I routinely use a couple of USB keys to transfer stuff between my 
host system and OLPC boards.  The ext2/3 has needed to be reformatted 
several times, whereas the FAT one is still using the factory format.

Owen Williams wrote:
> So I took a chance and bought a 4 gig SD card
> (http://www.newegg.com/product/product.asp?item=N82E16820163159).  
>
> I thought it wasn't working...
>
> Dec  6 17:11:10 localhost kernel: mmcblk0: mmc0:b368 SDC   4020224KiB 
> Dec  6 17:11:10 localhost kernel:  mmcblk0:<3>mmcblk0: error 1 transferring data
> Dec  6 17:11:10 localhost kernel: end_request: I/O error, dev mmcblk0, sector 0
> Dec  6 17:11:10 localhost kernel: Buffer I/O error on device mmcblk0, logical block 0
> Dec  6 17:11:10 localhost kernel:  unable to read partition table
>
> but then I ejected and reinserted and noticed /dev/mmcblk0
> and /dev/mmcblk0p1.  I mounted, and there it was:
>
> /dev/mmcblk0p1   3.8G   7.7M 3.6G 1% /media/4GSD
>
> Right now it's an ext2 drive, but I'd like to make it jffs2 instead.
> How do I create a jffs2 filesystem?  the documentation is really
> confusing and the mkfs.jffs2 wants to make a tree from existing files.
>
> owen
>
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