Howtoforge posted a tutorial about setting Up an active Samba CTDB cluster using GFS & DRBD on CentOS 5.5

This article explains how to set up an Active/Active Samba CTDB Cluster, using GFS and DRBD. Prepared by Rafael Marangoni, from BRLink Servidor Linux Team. We use two nodes, both are active nodes, and the requests are loadbalanced. To replicate data between the nodes we useDRBD. To active/active cluster, we must use a ClusterFS (in this case GFS), to make the two nodes to write on the DRBD resource at same time.

  Setting Up An Active/Active Samba CTDB Cluster Using GFS & DRBD (CentOS 5.5)