I bought this NAS in "does not work" state. At first, I thought that it may be something with PSU, or that flash was nuked after firmware update. Oh boy how wrong I was. I could tell whole story, ideas, and everything else I did before fixing it, but I will just tell You how to fix Your NAS if Your HDD's failed, and some modifications I did. I also plan to run buildroot on this machine in future (PowerPC and 1GB of RAM, sic!).
Whole fix is as easy as formatting random USB drive to FAT32, copying some files, and running NAS with new drives (drive) and USB drive inserted.
Before I saw Eligio's fix, I was trying things on my own. Using logic analyzer, I was able to find UART on motherboard. It is located on top of power button goldpins. UART talks on 115200 baudrate. (Right click -> "open image in new window" for bigger images)
BEWARE! UART on N150d works on 3.3V. I used cheap Wemos D1 platform to use as usb-uart adapter. You have to connect 3rd pin with ground, to disable ESP.
Original apps image has OpenSSH server, configuration, and even init script! Here's how to enable SSH and SFTP by default.
It's pretty nice how system installation works on this NAS. You have 3 packages: apps, config, and oem. They are unpacked to specific directories, overwriting them.
Buildroot has a nice toolchain that builds software which can run on our NAS. Only configuration you need to change is CPU Architecture -> PowerPC. From there, build any software you would like (htop does not read process list for whatever reason), and be ready to build new packages for Your installation. Create new directories for apps and config images. Copy original files from original packages (mount them using fusecram), and paste new software. I like to paste whole /lib and /usr/lib, since software from buildroot needs specific shared libraries. Now You can build new images using "mkfs.cramfs -N big", paste them onto your pendrive, and install new software on Your NAS.
