4 core vs 6 core processors are not typically something that small business owners think about. That said, as mentioned in Small Business Virtualization Example - How To Do It All On 1 Server, the way that server virtualization works is by using a more powerful processor and more memory to take on the jobs of several less powerful processors in distinct physical servers. These beefier servers also cost more. This increased initial outlay, however, means that your small business will spend less in operating costs as discussed in Will Virtualization Cost More Than A Standard Network Installation?
So, it is worth understanding, at least at a high level why more cores are critical to a successful server virtualization project. The more CPU cores there are in a server, the more virtual-server load can be handled at a high performance level. How to Set Up a Virtualization Server explains why the number of cores is generally even more important than processor speed in a virtualized environment.
Microsoft recommends using one core per virtual machine. Depending on the application running, we have experienced the need to run up to two cores per virtual machine (e.g. in the case of remote desktop services for a SQL-based ERP system). A good rule of thumb that we have seen empirically is that with a dual 6 core server, you may run up to 7 virtual machines and with a quad 6 core machine, you would be able to run 15 virtual machines.
So, it is not really a question of 4 core vs 6 core so much as understanding how many cores are really needed to handle all of the virtual machines on the server. Note that if we were talking about a true standalone environment, the only advantage to going to 6 cores over 4 cores would be if the application running on the server supported 6 core multi threading (this is not common).
How many physical machines could you virtualize?
Server virtualization requires more powerful processors and memory to consolidate multiple physical machines
In practice, more than one processor core is often required to handle a virtual machine
When not virtualizing, it would be unusual to need a 6 core processor
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