Raspberry Pi Cluster

The photo below shows my very tiny Raspberry Pi cluster. Built this to experiment with cluster/hpc computing. It use the ZP-088 "rack tower" from 52PI. This rack has space for four Raspberries. However mine contains three because I used the bottom one to power the fan and had to leave one space empty to fit the connectors. Normally you power the fan from the Raspberries on the top of the stack. But this one has in my case a Sense Hat and I wanted the led array to be visable.

Pi Cluster

The rack contains a model 3B and two times a model 2B. After the initial build I added more machines: two X86 machines, a model 1B Raspberry Pi Model 4 (visible in the back).

For work load management it uses Slurm The X86 machines run Ubuntu and the Slurm version in de Ubuntu repo does not match the version in the Raspian repo. Had to compile Slurm from source to fix this, which was an interesting exercise to be described in another article.

So now I have a seven node cluster with 29 cores.

$ sinfo
debug*       up   infinite      1  down* mungus
debug*       up   infinite      6   idle risdam[01-05],vidar

And can run commands in parallel:

$ srun -l -N6 hostname
0: risdam01
5: vidar
3: risdam04
2: risdam03
1: risdam02
4: risdam05

To monitor the machines I use RRDTool. This to keep track of CPU usage, network usage, and temperature. It revealed that the fan on the rack is pretty effective. Below a graph that shows the effect of turning the fan off and on again. Risdam02 - Risdam04 are in the rack. Risdam04 is right behind the rack.

Pi Temperatures with fan on and off

It shows an 10 degree temperature difference when turning the fan off.

The graph also shows the temperature difference between the different Pi models. Risdam02 and Risdam03 are each a model 2B. Risdam01 a model 4 and Risdam04 a model 3B.

The white line shows the room temperature as measured by the temperature sensor on the Sense Hat on Risdam04. When the fan is on the measurement is spot on, it is winter here and the termostat is set to 20oC. With the fan off the sensor is definitely way off the track. Observed a similar effect for the humidity sensor on the Sense Hat.

Ernie is included as a reference. Is the Raspberry Pi running the web server serving these pages. It is located in a different room.