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A low power 1U Raspberry Pi cluster server for inexpensive colocation.

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Raspberry Pi 1U Server

There are server colocation providers that allow hosting a 1U server for as low as $30/month, but there's a catch: There are restrictions on power usage (1A @ 120v max, for example) because they're expecting small and power-efficient network equipment like firewalls.

This repo is about designing a server that fits within the 1U space and 1A @ 120v power constraint while maximizing computing power, storage, and value.

raspberry pi 1u server - inside raspberry pi 1u server - front raspberry pi 1u server - back

TODO: calculate time to pay off vs R620

Table of contents

Colocation Providers

  • $30/month - Turnkey Internet
    • 1 Amp @ 120V
    • 1 Usable IP (+$10 for 5 usable IPs)
    • 10 Mbit Ethernet
    • 3 TB Monthly Transfer
  • $40/month - Nextarray
    • 100Mbps Unmetered
    • 1 Amps 120V
    • 3 Usable IPs (+$13 for 11 usable IPs)
    • GigE Port
    • 1.5Tbps Protection
    • Location: Dallas, TX
  • $50/month - Joe’s Datacenter
    • 5 Usable IPs
    • Bandwidth: 33TB on 1Gbps Port
    • Power: Up To 2 Amps 120V (Single Power Connection)
    • Network Connection: Single Network Cable
    • Location: Kansas City, MO

Parts

Specs Summary

  • 20x 1.5GHz CPUs
  • 16GB LPDDR4-3200 SDRAM
  • 1.2TB SSD Storage
  • Gigabit Ethernet

Total cost: ~$800

1U Chassis

Storage

Storage Enclosure

Switch

Single Board Computer

Raspberry Pi Case

  • 5x $12.99 - Geekworm Raspberry Pi 4 Armor Case
    • Allows access to GPIO pins, which will be necessary for the Pi wired to the relay for remote power management.
    • Uses less space than the Flirc case, which makes it difficult to close the chassis lid.
    • Reviews: 1

Power

Remote Power Management

Other Wiring

Power Usage

  • Raspberry Pi 4 + SSD:
    • idle: 0.44A @ 5V (0.018A @ 120v)
    • load: 0.84A @ 5V (0.035A @ 120v)
  • Total w/ blower fan on low setting:
    • idle: 0.30-32A @ 120V
    • load: 0.36A
  • Total w/ blower fan on high setting:
    • idle: 0.4A @ 120V

Software Setup

You will need to do this for each of the Raspberry Pi's:

  1. Flash an SD card with Raspbian Lite (under "Raspberry Pi OS (other)" in the Raspberry Pi Imager) and enable SSH with:
    1. cd /Volumes/boot/
    2. touch shh
  2. Insert the SD card into the Pi, power on, and ssh into the Pi with ssh pi@<ip address> and the password "raspberry".
  3. Update the hostname to correspond to the number on the case:
    1. sudo raspi-config
    2. 1 System Options -> S4 Hostname -> Update hostname -> Finish -> Reboot
  4. Update the firmware on the Pi to allow booting from USB:
    1. sudo apt-get update && sudo apt full-upgrade -y
    2. sudo rpi-update (only do this once on each Pi)
  5. Disable wifi and bluetooth:
    1. sudo bash -c 'echo -e "dtoverlay=pi3-disable-wifi" >> /boot/config.txt'
    2. sudo bash -c 'echo -e "dtoverlay=pi3-disable-bt" >> /boot/config.txt'
    3. sudo reboot
  6. Add your public key (while disconnected from the pi, with cat ~/.ssh/id_rsa.pub | ssh pi@<IP-ADDRESS> 'mkdir -p ~/.ssh && cat >> ~/.ssh/authorized_keys')
  7. Make sure the SSD into one of the blue USB 3 ports.
  8. SSH into the Pi again and Disable password authentication:
    1. sudo sed -i '/^#*PubkeyAuthentication /c PubkeyAuthentication yes' /etc/ssh/sshd_config
    2. sudo sed -i '/^#*ChallengeResponseAuthentication /c ChallengeResponseAuthentication no' /etc/ssh/sshd_config
    3. sudo sed -i '/^#*PasswordAuthentication /c PasswordAuthentication no' /etc/ssh/sshd_config
    4. sudo sed -i '/^#*UsePAM /c UsePAM no' /etc/ssh/sshd_config
  9. Configure the Pi to prioritize booting from the SSD:
    1. sudo raspi-config
    2. 6 Advanced Options -> A6 Boot Order -> B2 USB Boot -> Finish -> Reboot
    3. If you see an "No EEPROM bin file found" error, you may need to run sudo -E rpi-eeprom-config --edit and add [all] BOOT_ORDER=0xf14.
  10. Repeat the steps above (without sudo rpi-update) with the new OS on the SSD. SSH'ing into the new OS on the SSD may require clearing out the line with the corresponding IP in your ~/.ssh/known_hosts file with ssh-keygen -R <host>.

Hardware Setup

  1. Remove the hard drive bay dividers and front panel extension cable from the inside of the chassis.

    remove chassis dividers

  2. Install the Raspberry Pi's into their cases.

    install raspberry pi into geekworm case

  3. Install the M.2 drives into their enclosures.

  4. Insert a SD card into each of the Pi's.

  5. Add mounting tape to the bottom of each of the SSD enclosures and attach them to the top of the Raspberry Pi's.

    add mounting tape to ssd

  6. Add mounting tape to the bottom of the raspberry pi cases. Don't remove the bottom cover of the mounting tape adhesive yet.

    add mounting tape to raspberry pi

  7. Remove the rubber feet from the bottom of the networking switch and replace with 4x small squares of mounting tape. Don't remove the bottom cover of the mounting tape adhesive yet.

  8. Add labels with numbers to the tops of the cases. These numbers will correspond to the hostnames of the Pi's in the software setup.

    raspberry pi numbering

  9. Use wire cutters to remove the metal adjacent to the ethernet port and mount the port side of the ethernet extension to the back of the chassis with washers and the included bolts.

    installing ethernet port 1 installing ethernet port 2

  10. Cut the plastic piece that came with the chassis (for under the motherboard) to fit under the power supply breakout board.

  11. Drill holes in the chassis, insert nylon standoffs, and add the plastic sheet.

    installing atx breakout board 1

    installing atx breakout board 2

    installing atx breakout board 3

    installing atx breakout board 4

    installing atx breakout board 5

    installing atx breakout board 6

  12. Cut 10x 6" lengths of red standed wire, strip the both ends, and install one side of the wire end in the "+" slot of the USB terminal blocks and the other side into the 5V terminal blocks of the ATX power supply breakout board. Make sure the 20 pin power supply has a corresponding wire, some wires will be missing and may not actually work on the power breakout board.

    cutting wire for atx breakout board

    add usb connectors to atx breakout board

  13. Cut and strip 10x 6" lengths of green standed wires then install one side of the wire end in the "-" slot of the USB terminal blocks and the other side into the COM terminal blocks of the ATX power supply breakout board. Again, ensure the wire exists on the 20 pin cable before using the terminal block.

  14. Mount the ATX power supply breakout board and secure with nylon nuts. Insert the 20 pin ATX power supply connector into the ATX power supply breakout board.

    installing atx breakout board 7

  15. Remove the covers from the mounting tape adhesive on the bottom of the Pi cases switch and lay them in the chassis. Don't plug the power supply into the wall yet. You will probably want to try to match the layout from the finished project above, but this may change depending on how many Raspberry Pi's you have.

  16. Cut the 12V barrel connector along with 12" of wire off of the power adapter for the network switch. Attach the cable with the solid white line markings to 12V on the ATX breakout board and attach the other wire to a COM on the breakout board. You may want to confirm this is the correct "+" wire for your switch with an ohm meter and the diagram near the power connector the back of the switch.

    network switch positive negative

  17. Cut the piece plastic that came with the chassis (for under the motherboard) to fit under the 8 channel relay board.

    cut piece of plastic to fit under relay

  18. Drill holes in the chassis, insert nylon standoffs, and mount the 8 channel relay.

    installing relay 1

    installing relay 2

  19. Wire 4 of the 5 5V USB terminal "+" wires from the ATX breakout board to NC terminals on the 8 channel relay, and wire the other side of the relay to the "+" on the USB terminal block for 4 of the 5 Pi's. More relay setup instructions

  20. Drill holes in the chassis and insert nylon standoffs for the 1 channel relay.

    installing 1 ch relay part 1 installing 1 ch relay part 2

  21. Wire DC+ on the relay to a 3.3V GPIO pin from a Pi that is powered by the 8 channel relay. DC- will need to be wired to a ground GPIO pin and IN will need to be wired to GPIO pin 18. Finally, wire the 5V power from the ATX breakout board to NC, and wire COM to the "+" on the terminal block for the Pi isn't powered by the 8 channel relay.

    installing 1 ch relay part 3

  22. Mount the 1 channel relay to the chassis with the nylon standoffs.

    installing 1 ch relay part 4

  23. Move the jumper on the 1 channel relay from H to L.

  24. Plug one of ATX SATA power connectors into the fan controller and connect the blower fan from the chassis into the fan controller.

  25. Drill a hole in the front of the case for the power switch and install the power switch.

    power switch installed

  26. Add a 290 ohm resistor inline with a 6" length of wire with a jumper connector on one side, add heatshrink, and add that wire to a 3.3V terminal on the ATX power supply breakout board.

    wire front panel LED to the atx breakout board

  27. Add another wire of the same length with a jumper connector on one side to a COM terminal on the power supply breakout board, then put the jumpers onto the pins of the LEDs on the front panel.

    wire front panel LED to the atx breakout board

  28. Apply electrical tape over the unused header pins and terminal blocks to prevent accidental electrical shorts.

Network Setup

  1. Get the static IPs, subnet, and gateway from the colocation provider.
  2. Edit /etc/dhcpcd.conf on each of the Pis and add the networking info from the colocation provider, for example: 
    interface eth0
static ip_address=192.168.1.191/24
static routers=192.168.1.1
static domain_name_servers=8.8.8.8 8.8.4.4
  3. sudo reboot

Remote Power Management Software

Only do this on the power management Paspberry Pi connected to the relay:

  1. curl -o relay_control.py https://raw.githubusercontent.com/pawl/raspberry-pi-1u-server/main/relay_control.py
  2. Test the script: python relay_control.py

You should see the light on the SSD flash off and on for the Pi whose relay's GPIO pin you entered.

Measuring Amperage

  1. Plug the server into the Kill-A-Watt.
  2. Press the button on the Kill-A-Watt for "amps".
  3. sudo apt-get install stress
  4. while true; do vcgencmd measure_clock arm; vcgencmd measure_temp; sleep 10; done& stress -c 4 -t 900s
  5. Restart the server by unplugging and plugging back in. Watch the amperage on start-up.

Single Points Of Failure

  • Switch
  • Relay
  • Power Supply
  • Electrical Short (from loose terminal or pinched wire?)
  • The Management Pi Dies (and can't powercycle the other Pi's)

How Many More Pi's Will Fit?

At least 7. (including 1 Pi Zero and a Pi 3b)

7 raspberry pis in 1u server

Cloud Comparisons

This is a tough comparison to make because the Pi CPUs are only 1.5GHz per core.

AWS

  • T2.micro - $9.50/month for 1GB Ram & 1 CPU @ 2.5 GHz * 20 = $190/month
  • T2.medium - $38.00/month for 4GB Ram & 2 CPU @ 2.5 GHz * 10 = $380/month

The T2 instances have a limited number of CPU credits, which means they can't run at 100% all the time like the Pi can.

Digital Ocean

$20/month for 4GB Ram & 2 CPUs @ 2.5 GHz * 10 = $200/month

Ideas For V2

Other Colocation Options

Other Chassis Options

Other Single Board Computer Options

Other Case Options

  • No case, drill holes for stand-offs, and mount to the chassis.
    • More work, but would probably work fine and small heatsinks would be cheap.
  • Argon ONE M.2 Case for Raspberry Pi 4
    • Includes an M.2 storage adapter.

Other Storage Options

Note: I tried using 2.5" SSDs with inateck enclosures and there wasn't enough room.

Other Power Options

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