If you want to restore the original QNAP firmware for some reason, you can follow the instructions below. Please note that this will only work if your Debian system is still working. If your Debian system is broken but the machine itself works, you can use the recovery mode to restore the QNAP firmware.
First of all, you need a copy of the QNAP firmware. If you made a copy
of the flash partitions from your QNAP device, copy the backup files
mtd2 to your QNAP device. If you did not keep a copy, you can
obtain an image of the firmware from QNAP
and extract the files manually (make sure you obtain the correct file
for your model):
wget http://download.qnap.com/Storage/tsd/flashimage/F_TS-409_20081024-2.1.2.zip sudo apt install unzip unzip F_TS-409_20081024-2.1.2.zip dd if=F_TS-409_20081024-2.1.2.img of=mtd1 bs=1M count=2 dd if=F_TS-409_20081024-2.1.2.img of=mtd2 bs=1M skip=2 count=4
There are two steps to restore the original QNAP firmware. First, write the QNAP firmware to flash:
sudo modprobe mtdblock sudo dd if=mtd1 of=/dev/mtdblock1 sudo dd if=mtd2 of=/dev/mtdblock2
Second, you have to restart your QNAP, and then run QNAP Finder to install the QNAP software again. The second step is needed because the QNAP software is stored both in flash and on the hard drive and Debian removed the QNAP software when it formatted the disk.
After you put the QNAP firmware back in flash and installed the complete the QNAP software with QNAP Finder, your device will run the original software from QNAP again.