I had one I was about to throw away and thought to myself, I have another Nano 4GB that is working great. I wonder if I can use DD in the terminal (Linux) to fix the bad one (corrupted and not fixable since I do not have iTunes or Windows).
So, I plugged in both ipods and opened a terminal.
You can DD (clone disk) from one working ipod with RockBox to another that is corrupted using two USB cables plugged into a Linux computer. This is a great way to save a corrupted ipod.
MAKE SURE you copy the good one to the bad one. If in doubt, plug in one at a time and check using:
sudo fdisk -l
You will have to take ownership of the drive using chown (change ownership):
sudo chown <user> /dev/sdx
(of course change x to each actual ipod and own them one at a time)
Then just DD like this:
dd if=/dev/sdx of=/dev/sdx
(of course change x to the actual ipod location for the good (first) and corrupted (second)).
DONE! It works again (if you've done it correctly). Warning, if you DD a wrong location, you could clone the bad to the good one, or clone any other incorrect storage location to the ipod or the ipod to your computer etc. Use DD with caution!!