Setting up storage

When we started discussing the fundamental concepts of clustering, we mentioned that high availability clusters aim, in simple terms, to minimize downtime of services by providing failover capabilities. As we begin the journey of installing a web server and a database server in our cluster, we can't help but wonder how will we synchronize between nodes the content that those services should make available to us. We need to find a way for nodes to share a piece of common storage where data will be saved. If one node fails to provide access to it, the other node will take client requests from then on.

In Linux, a common and cost-free method of dealing with this question is an open source technology known as Distributed Replicated Block Device (DRBD), which makes it possible to mirror or replicate individual storage devices (such as hard disks or partitions) from one node to the other(s) over a network connection. In a somewhat high-level explanation, you can think of the...