April 12, 2011
The total capacity of all guest virtual machines is lower than the total capacity of non-virtualized host server. Virtualization can be compared to cutting a whole pie into individual pieces. Two exceptions:
- It's impossible to divide hardware components among virtual machines and they will always be shared.
- The pie slices altogether have the same number of calories as a whole pie, but the total capacity of all guest virtual machines is lower than the total capacity of non-virtualized host server.
Here's a recap of an explanation on how the queuing theory results are in line with our experience:
- Toll plaza with booths equally accessible by any cars has lower congestion than the same plaza with booths divided by two categories: ones serving only sedans and the others serving only trucks. An intuitive explanation is: in a non-divided plaza in an absence of the trucks a sedan can be processed by any booth and vice versa; in a divided plaza the booths dedicated to trucks will stay idle even if there is a queue of sedans.
- Movie theater box office: if any window serves any theatergoers, then waiting queue is not as long as in a case when some windows provide only to particular customer categories.
If your company has joined the journey toward virtualization and cloud computing make sure it also has joined a journey toward system performance measurement and capacity planning to ensure smooth sailing.
It is important to have careful capacity plans in place when sizing virtual machines. You need to understand the differences between physical and virtual machines.