The primary requirement for an Active/Active cluster is that the data required for your services is available, simultaneously, on both machines. Pacemaker makes no requirement on how this is achieved; you could use a SAN if you had one available, but since DRBD supports multiple Primaries, we can continue to use it here.
9.1. Install Cluster Filesystem Software
The only hitch is that we need to use a cluster-aware filesystem. The one we used earlier with DRBD, xfs, is not one of those. Both OCFS2 and GFS2 are supported; here, we will use GFS2.
On both nodes, install the GFS2 command-line utilities and the Distributed Lock Manager (DLM) required by cluster filesystems:
# yum install -y gfs2-utils dlm
