Since the release of ESX Server over 12 years ago, the IT landscape has changed dramatically with a massive shift away from the old physical datacenter to today’s virtual datacenter. As the technology matured and complexity of systems increased so did the requirement for administrators to rethink the way they manage their systems. When it comes to VM resource allocations unfortunately there are still many administrators today who are stuck with the old mentality of administering their virtual servers as if they are physical.
A VMs resource allocation should be based on real data and not guesstimates, the vCenter performance charts provide a heap of data to be able to make informed decisions on the VMs vCPU and memory allocations. It is always best following VMware best practice by starting out with the least amount of resources and then increasing where required, remembering in virtualization usually less is more. I constantly see administrators blindly adding more vCPUs in a bid to improve the VMs performance only to degrade it by increasing physical CPU contention which can be witnessed by the rise of CPU ready time. Out of desperation they will then double the memory allocation in the hope that things will magically improve, unknowingly they are not only degrading the performance of that particular VM they have the potential to effect the performance of the rest of the virtual environment.