Monitoring CPU Usage
When monitoring a VM, it's always a good starting point to keep an eye on CPU consumption. Many VMs started out in life as underperforming physical servers. One of VMware's most successful sales pitches was being able to take all those lackluster physical boxes that are not busy and convert them to VMs. Once they are converted, virtual infrastructure managers tend to think of these VMs as simple, lackluster, and low-utilization servers with nothing to worry over or monitor. The truth, though, is quite the opposite.
When the server was physical, it had an entire box of hardware to itself. Now it must share its resources with many other workloads. In aggregate, they represent quite a load, and if some or many of them become somewhat busy, they contend with each other for the finite capabilities of the ESXi host on which they run. Of course, they don't know they are contending for resources because the VMkernel tries to make sure they get the resources...
