Rebecca Grider, who works at the performance engineering department at VMware posted an article on the VMware VROOM! Blog about performance scaling of an cluster which is build on entry-level hardware. Using VMmark they determined how a four-host cluster with a modest hardware configuration, the Dell PowerEdge R310 running ESX 4.1. would scale under increasing load.
Since most of the times the workload throughput is limited by disk performance the tests were repeated with two different storage arrays, the EMC CX500 and the EMC CX3-20.