tl;dr - Many people love 2-node clusters because they seem conceptually simpler and 33% cheaper, but while it’s possible to construct good ones, most will have subtle failure modes

The first step towards creating any HA system is to look for and try to eliminate single points of failure, often abbreviated as SPoF.

In the past I setup some new Pacemaker clustered nodes with a fresh Debian Stretch installation. I followed our standard installation guide, created also shared replicated DRBD storage, but whenever I tried to mount the ext4 storage DRBD detached the disks on both node sides with I/O errors. After recreating it, using other storage volumes and testing my ProLiant hardware (whop I thought it had got a defect..) it still occurs, but somewhere in the middle of testing, a quicker setup without LVM it worked fine, hum..

github source

The LCMC is a GUI application that configures, manages and visualizes high-availability clusters. Specifically it manages clusters that use one or more of these components: Pacemaker, Corosync, Heartbeat, DRBD, KVM, XEN and LVM.