OS Re-install via SSH

Also note that if you do a factory reset, you will have to clic on the backup button anyway... So ok for reinstall, but that's a bit pointless for factory reset. Also be aware that network setting being reset you'd better have either a DHCP reservation or knowing where to look to find the new IP once rebooted (that said if network setting are not rewetted like mdgm said...).

I'd like an option to do a factory reset without losing the data, but knowing how the OS is built, I'm not likely to see it, the only way I found was to erase the system partition, reboot and reinstall the OS. Something I'm not comfortable to do although I guess booting without OS isn't much different than plugging empty drives for first boot and shouldn't represent a risk for the NAS itself. That said I'm not so sure that the raid config will be ok, so there is a real risk for the data.
Still linux is quite good for that kind of things, having a list of file to replace and the ability to extract the OS-image from flash and you could replace anything and erase file that are not on the list while retaining some configs (like raid, share list...) but that's a hell of a script to do (well the script itself isn't that bad but the testing and the management of the exclude list will be a nightmare).