Last stock firmware version (V5.21(AASZ.5)C0) for NAS520 wanted

@Mijzelf, hhi can u upload these files again? because i need repair my NAS from bad files. plz and thx for u effort

there is a https://zyxel.ddnss.eu/Users/Mijzelf/Firmware/NAS520_V5.21(AASZ.5)C0.zip

but that is rather update file. do u have full restore firmware for that nas 520.?? thank u for u effort :)

ok,

Hi everyone!I decided to breathe new life into the old Zyxel NAS520. While this hardware is a bit dated, it’s still very capable if you get rid of the stock firmware. I've prepared a custom Debian 11 (Bullseye) image with OpenMediaVault 6 and a modern 6.6.x Kernel.Why this setup?
Most NAS520 builds run entirely from HDDs, which prevents them from sleeping and makes the OS sluggish. My release uses a Hybrid Boot approach:

1. OS on SD Card: The system is snappy and silent.
2. Data on RAID 1: Your HDDs are used strictly for storage.
3. True HDD Spindown: Because the rootfs is on the SD card, your hard drives can finally sleep properly when idle.
4. Stability: I've implemented a Real-Time Watchdog script (FIFO 99) to ensure the NAS never reboots under heavy load (like RAID resyncing).

What’s inside the folder:

• System Image: Pre-configured and ready to flash.
• Kernel (uImage): Modern 6.6+ build for NAND.
• README.txt: Full step-by-step instructions (Barebox commands, credentials, etc.).

Download Link (Mega.nz):
👉 https://mega.nz/folder/zwIUiaAZ#dWQR1B-A20QjlfZXmADpuQCredentials:

• User: admin
• Password: lol (for both SSH and Web GUI)

It was a long road of debugging UART and Barebox, but the result is a rock-solid, silent, and modern NAS. I hope this helps anyone still holding onto this great piece of hardware!

ps. man…. it took me about 7 days…servators images but mostly builded and config using

Image for Zyxel NAS520/NAS540/NAS542 with Kernel 6.6.84, Debian 11 and OMV 6.9:

https://seafile.servator.de/nas/zyxel/images/debian-nas-bullseye-25.311-armhf.img.gz

for servator owner: thank u also for ur great work , but these image are not specyfilay for nas 520… :D

i made massively optimization of rootfs. I will upload rootfs img today after work.

Well, here's my opinion: the kernel with Servator patches works great, but OMV is too heavy for a NAS520. The maximum transfer rate I've managed to achieve is 60-70 MB/s with a 1 GB file. My optimizations simply involve disabling and muting many monitoring services that consume CPU cycles. and remember rootfs is placed on sd card not hdd. I would like to have all hdd space to raid data than partitioned to roofs and data with raid.

well kernel and rootfs are from :

persons github https://github.com/scpcom/debian-nas-build/releases

https://seafile.servator.de/nas/zyxel/images/debian-nas-bullseye-25.311-armhf.img.gz

but this image turned out to be incomplete, in the systemd sense (it was replaced with some useless script) and is not adapted to the NAS520( kernel is patched to comcerto2k and gpio everything is fine, but rootfs needed massively adjusting to nas520) only to more powerful hardware.