On a Virtual Machine, the following two values are associated with RAM:
Allocated RAM (ARAM)
Reserved RAM (RRAM)
If RRAM is less than ARAM, VMware creates a file of size ARAM - RRAM, and uses the file as RAM if there is contention for RAM resources. The performance is impacted as you switch from RAM I/O to file I/O. Therefore, you must always reserve ARAM.
CPU
Ensure that Hyperthreading is turned on.
Ensure that CPU meets or exceeds the benchmark rating for Intel Xeon E5-2697 (first edition) 2.60GHz.
Refer to VMware documentation for information about interpreting esxtop statistics, to allow you to investigate and avoid performance problems at the virtualization layer.
Observe the following counters for using esxtop data at the host level:
CPU Load Average: A load average of 1.00 indicates that the physical CPUs of the host are fully utilized. A load average of 0.5 indicates that the physical CPUs of the host are half utilized. Any value greater than 1 indicates performance problems.
Note:
Performance problems can also occur with values less than 1.
Physical CPU: Ensure that the Physical CPU usage does not exceed 80%. Performance is impacted if the Physical CPU usage consistently exceeds 80%.
Observe the following for using esxtop data at the Virtual Machine level:
RDY: The percentage of time that something is waiting for a CPU to be available to run its workload. Ensure that RDY does not exceed 5% for any vCPU.
MLMTD: The percentage of time that a vCPU was waiting due to a limit set on the Virtual Machine for CPU usage. Ensure that you increase or remove your limit if this value is greater than 0.
A lot of data is available through esxtop and VMware Infrastructure Client for all levels of granularity, from host through Virtual Machine and per vCPU.
