I got my c3100 about a week ago and have been doing a lot of experimenting with it. I was very interested in doing video, so I installed Tetsu's special kernel almost right away, and it seemed to be working OK. However, I had some problems that lead me to believe that the current version of the special kernel may not be stable (and admittedly Tetsu says that it may not be stable on his site). I am still a Linux newbie, so I'm not sure if what happened was due to my bungling or because of the special kernel. Maybe I can get some input on that from the gurus here
Anyway, my first problem came when I mounted a shared folder to somewhere on /hdd3/ (I can't recall the exact location). I was trying to get things on the shared disk to show up in the Zaurus apps and file browser, and it did work until I opened up the pdf viewer. It seemed to hang the zaurus and so after a few minutes I decided to just remove the battery and reset the Z. When it rebooted, I got a error messages ending with "HDD1 ERROR!! Unable to open LED device" and the Z wouldn't boot any further. I eventually had to reboot the Z holding the OK button and do a factory restore. I was surprised to see that the internal microdrive is erased by this operation. There doesn't seem to be a way to restore the device to the factory settings while preserving the contents of the MD. But anyway, I was still in the middle of installing and experimenting, so I didn't have a backup, but all I lost was some time.
A couple of days later (today) I had another problem. This time I simply chose "reboot" from the QT menu and the Zaurus hung during booting, complaining about a disk being read-only or something (I neglected to write down the messages). I had mounted a shared folder a while before this happened, went offline and removed the network card to insert my CF microdrive. Could not unmounting the folder properly have this effect? I had to do a factory restore again, and again I lost what was on the internal MD, although I did have a backup of the internal memory.
Needless to say, this is disturbing to me. I have returned to the Sharp kernel for now to see if that affects things. Does anyone have any ideas about what might have caused these two problems?
A couple of notes about doing a NAND restore. I found several threads and web sites detailing the process for doing this, but I couldn't get it to work for the longest time. However, I finally figured it out, so I thought I would put it here in case anyone else has similar problems.
To restore the NAND, you first need a NAND backup file. I downloaded mine from conics.net, I believe, although you can do a backup yourself of course. You need to put the backup file (named SYSTC310.DBK) on a CF card. The card has to be big enough for the backup file, obviously, so it needs to be larger than a 128MB card (the file is around 132MB). I had some trouble here, because I had originally used a 2.2GB MAGICSTOR microdrive to install the special kernel, but it would not work for the NAND restore. I don't know why. It was FAT formatted and otherwise worked fine in the Zaurus. Anyway, I dug up an old 340MB IBM microdrive and put the backup file on that, which worked.
To do the NAND restore, you have to remove the battery, the power supply, and any memory cards and wait for a few seconds. (This is where I had a problem. The menu won't come up if you have the CF card in the Z while doing this.) Then hold down the D and M keys on the keyboard and put the battery back in. (Don't release the D and M buttons until the service menu appears.) Move the battery switch to the ON position and plug in the AC adapter. The service menu should have come up.
Press the "up" arrow twice to get to page 3 of the menu (it will appear to be the "right" button if you're holding the Zaurus vertically). Insert your CF card. Select the "NAND Flash Restore" option and press OK. It will say something like "NAND Flash Restore from CF" and then it will indicate that it has found the backup file. (When I was using the MAGICSTOR microdrive, it would hang at the "NAND Flash Restore from CF" message and do nothing.) Then press OK twice to confirm and watch the progress display at the bottom of the screen. When it says "Restore...OK" you can press cancel to get back to the service menu, and then remove the battery and power supply to reset. Put them back and power back on, and you should see the Zaurus boot.
So to sum up, make sure you don't have a CD card in the slot when trying to bring up the service menu, and if it doesn't find your backup file on the CF, try using a different card.