Working with your SD card

What can you do with your SD card?

Recall a typical memory and filesystem layout if you happen to have an SD memory card:

   Device            FS type     Device name      Mount      Usage(?)

16M writable flash    jffs2     /dev/mtdblock4    /           75%
64M RAM:
    40M memory	
    24M storage       ext2      /dev/mtdblock6   /mnt/ram     0%
64M CF card           vfat      /dev/hda1        /mnt/cf      0%
64M SD card           vfat      /dev/mmcda1      /mnt/card    0%
   

From the above, you can see that SD cards come, by default, formatted with a VFAT filesystem and, if you want to store data on them, you can always do that explicitly by copying that data anywhere under the mount point /mnt/card. However, you can go considerably beyond that.

If you want to use the storage on the SD card as an extension of the operating system, you can reformat the card with an ext2 filesystem, then start copying system directories to the card and creating symlinks to the new locations.

Some of the system directories, such as /home, /root and /opt are fairly easy to shift from flash to the SD card. Others, like /usr, are a little trickier. All of this is explained on the next few pages.