Home/ Build Cluster/ Prepare micro SD Card
Phase 1 — Build Cluster · Step 2 of 14

Prepare micro SD Card with Raspberry Pi OS

Flash Raspberry Pi OS onto each of your 4 SD cards using the official Imager. You need one card per node.

Download the Official Imager

Raspberry Pi Ltd provides a cross-platform GUI tool called Raspberry Pi Imager that handles downloading the OS and writing it to the SD card in one step.

Download it from the official page:

https://www.raspberrypi.com/software/

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Available for Windows, macOS and Ubuntu/Debian. Install it on the computer you'll use to flash the cards, not on the Pi itself.

Choose the Right OS

In the Imager, select:

  • Raspberry Pi OS (64-bit) for the Pi 4 MASTER node — better performance with the ARM64 kernel.
  • Raspberry Pi OS (32-bit) for the Pi 3 B+ SLAVE nodes — maximum compatibility.
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Architecture matters for Docker images. The Pi 4 running 64-bit OS uses arm64/aarch64. Pi 3 running 32-bit uses armv7l / armhf. Make sure you pull Docker images tagged for the right architecture.

Flash Steps

  1. Insert the micro SD card into your USB adapter and connect to your computer.
  2. Open Raspberry Pi Imager.
  3. Click "Choose OS" → Raspberry Pi OS.
  4. Click "Choose Storage" → select your SD card.
  5. Click the ⚙ gear icon (Advanced Options) — set hostname, enable SSH, set a username/password, and optionally pre-configure WiFi.
  6. Click "Write" and wait for the process to finish.
  7. Repeat for all 4 SD cards (use a different hostname each time: MASTER, SLAVE1, SLAVE2, SLAVE3).
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Pre-configure SSH in the Imager — this saves you from needing a keyboard and monitor. Just insert the card, boot the Pi, and SSH straight in from your laptop.

Verify the Flash

The Imager automatically verifies the written data. If verification fails, try a different SD card — low-quality cards are a common source of random cluster failures.

2× Backup Cards for MASTER

The parts list includes 6 SD cards for 4 nodes. Keep 2 spares as full backups of the MASTER card. You can clone a card using the Imager's "Backup" option, or on Linux with:

Clone MASTER SD card on Linux
sudo dd if=/dev/sdX of=master-backup.img bs=4M status=progress
# Restore from backup:
sudo dd if=master-backup.img of=/dev/sdX bs=4M status=progress

Replace /dev/sdX with the actual device path (check with lsblk).