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Create a high availability VM with DRBD9 and Reactor

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Article from ADMIN 89/2025

By Martin Loschwitz

DRBD9 and DRBD Reactor create a Linux high-availability stack for virtual instances with replicated storage comparable to the classic Corosync and Pacemaker solution.

In today's IT landscape, everything has to scale: Bigger, better, more is the saying. However, this does not mean that classic high availability (HA) in the form of two-node clusters is a thing of the past. Usually, a legacy HA cluster steps in to ensure that central services required for platform operation survive failures and other issues. In some cases, the required services run directly on dedicated hardware with Linux, but it is far more common to assign the service to virtual instances and let a cluster manager manage them.

The combination of DRBD, Pacemaker, and KVM with Libvirt is established and reliable but not particularly popular, mainly because of the Linux HA stack (see the "Linux HA Stack" box). DRBD is a convenient alternative for most administrators. On many sites, you will find DRBD9 instead of DRBD8. The newer version is just as easy to use and configure in terms of basic configuration.

Linux HA Stack

Fifteen years ago, the world looked very different when it came to Linux and clusters. Heartbeat, developed primarily by Alan Robertson at IBM, was little more than a mess of shell scripts that could restart services on another server in the event of a server failure; then, the stack caught the attention of the major distributors. First, SUSE commissioned Andrew Beekhof to develop Heartbeat [1] into a full-fledged cluster manager, which became known as Heartbeat 2. Beekhof then joined Red Hat, where he was tasked with integrating various features into Heartbeat that would enable the operation of clusters with more than two nodes. Soon, the project changed its name to Pacemaker.

Pacemaker has become increasingly complex since then. Not only does it still rely on a configuration file under the hood that in turn relies on XML and is correspondingly complicated to use, the

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