Customer with small vSphere environment of just two hosts had performance issues and they asked me to investigate the situation. When looking at the technical specs at first glance, you would suspect that this configuration should work. With just two hosts, each dual Quad core CPU, the enivornment had a total of 16 CPU cores. In total there were only 9 VMs running using a total of 23 vCPUs. Usually you can easily run 5 vCPUs per core, if not more.
Turned out there were a number of VMs with 4 vCPUs and 2 vCPUs that really didn’t need them. You can easily discover this by checking READY en CO-STOP value in the vCenter performance charts. Go to the performance tab of your vSphere host and select advanced. Then select “Chart options” go to the CPU section, choose the “realtime” section and then on the right deselect all counters and only select “Ready” and “Co-Stop”. Click OK.
To learn more and to read the entire article at its source, please refer to the following page, How too many vCPUs can negatively affect your performance- Gabes Virtual World - gabesvirtualworld.com