While planned migrations are always preferred, sometimes hardware failures or server instability will introduce an aspect of surprise. If we had not used Pacemaker, a server crash would be a catastrophic event. Even if we had followed every chapter in this book this far and had Nagios, the full TIG monitoring stack, and email alerts galore, a DBA would need to be available to activate the alternate node.
If an outage occurred at night when everyone was sleeping, we would be faced with a worst-case scenario. The necessary personnel might not hear the alert for several minutes, and more time would be lost on triage and activation steps. Such an outage could extend from a few minutes to over an hour. So much for our high availability!
Yet at this point, we don't know whether Pacemaker would negate the preceding scenario. While we've tested...