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Raspberry Tau: a Pi cluster

The Raspberry PI is a small ARM computer (hardware specifications in wiki, outline and FAQs). Of course, you can build a cluster with it!

As 2π is proposed to be named τ we’ve chosen the name “Raspberry Tau” for this proof-of-concept.

We’ve connected two Raspberry Pis via their on-board ethernet interfaces (via a switch, so we can simply SSH into them), booted via 2GB SD-cards with a Raspbian image on them. After upgrading to a kernel that has kernel-headers available we built DRBD modules, and voilá! A Raspberry Tau cluster is born.

We’re replicating the data on the USB-Sticks; their performance nicely matches the available network. Here’s /proc/drbd (shortened and line-wrapped for readability):

root@raspberry-alice:~# cat /proc/version 
Linux version 3.2.0-3-rpi (Debian 3.2.21-1+rpi1) 
  ( (… Debian 4.6.3-1.1+rpi2)…)
root@raspberry-alice:~# cat /proc/drbd 
version: 8.4.2 (api:1/proto:86-101)
GIT-hash: 7ad5f850d711223713d6dcadc3dd48860321070c build by
    root@raspberry-bob, 2012-09-18 12:58:08
 0: cs:Connected ro:Primary/Secondary ds:UpToDate/UpToDate C r-----
    ns:805304 nr:0 dw:348628 dr:818596 al:127 bm:70 lo:0 pe:0
      ua:0 ap:0 ep:1 wo:d oos:0

As Raspbian is Debian-based, there are Pacemaker (and Heartbeat resp. Corosync) packages available … so a cheap, low-power, High-Availability cluster is easily built.

Disclaimer: for a real HA-cluster you’d need a few more things.

  • a STONITH device (if power is supplied via a Linux-PC, you could turn off the USB port by software), and
  • redundant network connectivity (USB ethernet adapter).

Of course, if you’re just clustering your media library these things might not be mandatory.

Packages are available for everyone – just drop an email to, and we will be happy to provide them. Please note that the upstream kernels already include the DRBD kernel module, so there’s no need to compile your own – unless you want to test the cutting edge; in that case, good luck 😉

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