Server consolidations trends

Network World published an article providing some interesting values on server consolidation trends:

…When companies first apply virtualization, the average ratio is around 15:1. After one year it drops to 8:1 and after three years stabilizes at an average of 3:1. In order to fit 15 to 20 virtual machines on a single server, the average CPU utilization of these virtual machines must be 5% to 8%. These represent servers with permanently low demand on CPU resources or with intermittent demand: testing and development servers, small Web servers with many static pages, rarely used applications, and so forth….

Read the whole article at source.

I would say this values could be misinterpreted.
One thing it’s true: when a company embraces server virtualization starts loading the virtual infrastructure with low resources-demanding services, typically web servers, DNS, DHCP and others. This approach easily leads to achieve 15:1 or 20:1 ratios. After that 2 kind of things can happen:

  • the company grows and virtualized services start demanding more host resources. In this case, with the same physical hardware available, less virtual machines can be allowed to run concurrently.
  • the company is convinced virtualization is cost-effective and reliable enough and start moving in the virtual infrastructure also more critical services like mail servers, databases, and other hungry-resources services. Also in this case the amount of virtual machines allowed per host has to decrease.

In both cases the initial VMs / host ratio decreases, even reaching bottom values of 3:1. But what is unsaid, and Network World is missing to report, is that companies experiencing such scenarios 99% of times buy more physical servers to redistribute all virtual machines running. So the final server consolidation ratio should be calculated among all available hosts.