An open hardware offsite backup appliance based on the Raspberry Pi CM4. A custom carrier board with a PCIe SATA controller, Gigabit Ethernet, and a battery-backed RTC — designed to be left at a trusted location and managed remotely.
Plug in Ethernet, plug in power, done. The device receives encrypted backups over WireGuard, spins down the disk when idle, and costs nothing to operate after the initial build.
Key specs:
- ASM1061 PCIe Gen 2 x1 to dual SATA III — no proprietary firmware required
- Gigabit Ethernet with integrated magnetics (Hanrun HR911130A)
- DS3231 RTC with battery backup for scheduled wake/sleep
- 12V DC input supporting both 2.5" and 3.5" SATA drives
- USB-C OTG for eMMC flashing and initial backup seeding
- 4-layer PCB with impedance-controlled differential routing, designed in KiCad 10
- ~€125 BOM cost — pays for itself in under two years vs. cloud backup
Hardware documentation is auto-generated via CI: laenzlinger.github.io/granit
Licensed under CERN Open Hardware Licence v2 — Permissive.
This project grew out of my Home NAS Infrastructure — the offsite backup currently runs on a CM5 with a USB-to-SATA cable. Granit replaces that with a dedicated board.