Recovery mode for QNAP devices available now

QNAP recently released an upgrade for u-boot, the boot loader used on most QNAP devices, that adds a recovery mode. With this recovery mode, a backup image is requested via TFTP and then written to flash. This is useful in case there are problems during the installation or an upgrade of Debian.

While Debian itself works well on QNAP and another NAS devices, we get reports from users every once in a while that their machine stopped booting (either after an upgrade or for no good reason) and it's usually impossible to say why since these devices are headless. The recovery mode allows them to put an image into flash that is known to work or an image of the installer that can be used as a rescue option. Essentially, the recovery mode removes the need for a serial console in many cases.

I've added information about the recovery mode for the QNAP TS-109, TS-209 and TS-409/TS-409U, including installation instructions of users already running Debian.