Virtual Machine evaluation-how to determine the number of virtual machines deployed on a CPU core?

A recent study of virtualization technology inevitably encountered a problem: how to evaluate the capacity of virtual hosts on physical hosts? The ideas in the following article are enlightening.

How to determine the number of virtual machines deployed on a CPU core?

Abstract:This article describes the ideal number of virtual machines deployed on a CPU core.

Users often ask me this question: "What is the ideal number of virtual machines deployed on a CPU core ?" I try to answer one of the following two answers: either the user makes a decision based on the test instance in the industry, or verifies the performance and evaluates the CPU demand based on their own desktop PC.

According to industry standards, a GHz quad-core dual-CPU server can usually load 30 to 80 virtual machines, and the number of different factors is that the office desktop type is different.

Lightweight users: the pre-period value for CPU resources is 300 MHz. Such users may be vending machine operators, receptionists, administrators, or web users only. This type of user's office desktop may be suspended or not in use at all, so the configuration of the server per core ratio is approximately 10:1.

Medium users: the expected CPU usage value is 500 MHz. Such users may include data entry personnel, doctors, students, Microsoft Office users, and telemarketers who use internal company applications, or the service desk staff. These users only use their office desktops during working hours. As a result, the ratio of servers with that configuration is approximately 6:1.

Heavyweight users: the expected value for CPU resources is 800 MHz. Such users may include developers, system administrators, IT staff, database administrators, or engineers. Such users have a high workload on their office desktops during normal working hours or after work hours. They may need to run a large number of graphics processing tools or Java applications, which will increase the burden on the office desktop. As a result, the ratio of servers with that configuration is approximately 3.75: 1.

Super heavyweight users: the expected value for CPU resources is 1 GHz. Such users may use large graphics processing tools, such as CAD users or graphic interface developers. There is another type of developers who process Java or web designs with high CPU usage. This type of user desk usage is usually maintained at a high level, so the configuration of the server per core ratio may be close to 2:1.
　　
If you use this evaluation system to design a VDI architecture, you need to know that all these users are mixed in the entire work environment. And because they prefer to require more consuppability than CPU, they must also consider the memory and disk space.

Another way to plan a virtual desktop architecture is to collect data from the office desktop in the actual working environment and perform basic analysis and computing on the data.

If a standard desk faces a 2.5 GHz Single-core CPU usage of 10%, the office desktop uses an average of 250 MHz. The peak time usage is 25%, that is, 625 MHz, but only 20 minutes in a day. Based on this time measurement standard, we consider using the average utilization time.

Tip: Virtualization of these office desktops requires a small amount of system overhead to run some components, such as virtualized graphical interfaces, sound and other devices that need to be connected. We assume that the system overhead will increase by 25% for each office desktop.

Therefore, the calculation is as follows: 250 MHz * 30% = 75 MHz

Then there are 250 MHz + 75 MHz = 32 MHz

If we use a 3.0 quad-core dual-CPU server, the following formula is obtained:

(3.0 GHz * 8)/325 MHz = 73.85 office desktops.

You must know that these computing equations are not very scientific, and only practical tests can provide accurate data. However, for most users, these computing results are very close to the exact number, and they can provide the necessary help when planning the virtual desktop architecture.