Given the prevalence of High-Availability Clusters today, we look at how much actual extra availability they provide compared to a single server in the face of a set of common failures. We compare three HA clustering solutions, AIX, Windows 2000 Advanced Server and Red Hat Linux. We measure “uptime” of the HA cluster and compare it with a similar non-HA configuration. While looking strictly at performance as a measurable value determined by the success of http clients’ attempted connections, other aspects of HA clustering that are of concern to system administrator and network architects are examined as well.