How do Server Virtualization, CPU Utilization and IT Utilization Efficiency relate

When talking about virtualization in a Data Center and how it effects CPU utilization and Efficiencies I find myself often in a debate about definitions and not getting to the substance… So I thought it might be helpful to define some simple terms and formulas here. I promise its simple math.

On the server level, this measure of how many virtual servers are hosted on one physical server is commonly used:
# Virtual servers on one physical server (SVP);
keep in mind, that server is no longer available as a stand alone server

On the data center level:
These terms are typically used:
# Total available Servers in Data Center (ST)
# Physical Servers hosting Virtual Servers as a subset of # physical servers (PSV)
# Virtual Servers in Data Center (SV = PSV*SVP)
# Physical Servers in Data Center (SP = ST + PSV – SV)
% Virtualization Degree in Data Center (VDDC = SV/ST)

As an illustration, assuming a Data Center has the need of 1000 total servers, dependent on the virtualization choices (yellow fields) results in a significant difference in how many physical servers are needed (and generate Green House Gas Emissions).

There are two more items to consider the CPU utilization and Server Utilization Efficiency. You can read more on those here, simplistically they describe how busy the server is (CPU) and how efficient it is able to convert electricity into IT work.

Typically servers with no virtualization have a CPU utilization of 10% or less, pretty low. With virtualization this can be increased and a 40% utilization is desirable. I assumed that 10 virtual servers on one physical server gets you to 40% CPU utilization, but that might be different in your data center depending on your servers and applications.

In the table above I made the assumption we start CPU utilization at 10% in average across all servers and as we implement more virtualization in average we get to 40%, proportional to VDDC increasing. With that the servers get significantly more efficient and ITUE grows in average to 52%. These are general examples and your environment may be very different.

Purpose was to give you a quick framework on how all these values and definitions work with each other. Hope this is helpful.