Compute Resources for VMware vSphere Cloud Infrastructure

This article explains on how to estimate required number for VMware ESXi hosts to setup your own VMware vSphere cloud infrastructure.

To determine the required number of VMware ESXi hosts that is needed to consolidate virtualization candidates, performance and utilization can been analyzed using VMware Capacity Planner.

VMware ESXi Host CPU and Memory Requirements

For this exercise let’s assume as a result of CPU and Memory analysis we have got the following performance requirements. For our analysis we have considered primarily the resource utilization for each system, including average and peak CPU and memory utilization.

Performance Metric	Requirement
Average number of CPUs per physical system	2
Average CPU MHz	2500 MHZ
Average CPU utilization per physical system	12% (300 MHz)
Average peak CPU utilization per physical system	36% (900 MHz)
Total CPU resources for all virtual machines at peak	200,000 MHz
Average amount of RAM per physical system	2000 MB
Average memory utilization per physical system	50% (1000 MB)
Average peak memory utilization per physical system	65% (1300 MB)
Total RAM for all virtual machines at peak (no memory sharing)	250,000 MB
Assumed memory-sharing benefit when virtualized	25% (*)
Total RAM for all virtual machines at peak (memory sharing)	187,000 MB

Now we can start estimating number of ESXi hosts that is required to support the workloads.

ESXi Host CPU Specifications

Using the performance data above along with CPU and RAM requirements, it is possible to derive the high-level CPU and RAM requirements that an ESXi host must deliver. Let’s say the following table provides high-level CPU specifications details of the chosen ESXi server.

Attribute	Specification
No. of CPUs per host	2
No. of cores per CPU	8
MHz per CPU core	2,200 MHz
Total CPU MHz per CPU	17,600 MHz
Total CPU MHz per host	35,200 MHz
Proposed maximum host CPU utilization	80%
Available CPU MHz per host	28,160 MHz

ESXi Host Memory Specifications

Similarly you need to perform analysis on high-level memory specifications. Let’s assume you have chosen an ESXi Server which comes with 96GB configuration which provides sufficient capacity for the requirements and still allow room for growth.

Attribute	Specification
Total RAM per host	96,000 MB
Proposed maximum host RAM utilization	80%
Available RAM per host	76,800 MB

ESXi Host Requirements

So based on the above high-level CPU and Memory specifications we can derive the minimum number of ESXi hosts required from the perspective of both CPU and Memory.

Type	Total Peak Resources Required	Available Resources per Host	ESXi Hosts needed to Satisfy Requirements
CPU	200,000 MHz	28,160 MHz	7
RAM	187,000 MB	76,800 MB	3

VMware ESXi Hosts Required for Project

Let’s say if we anticipate the growth rate of 20%, then the following table shows the required number of hosts for our vSphere environment.

No. of ESXi hosts required	Percentage of growth anticipated	Availability requirements	No. of ESXi hosts required
7	20%	N+1	10