The survey found that, on average, administrators allocate 70% of a server's RAM to virtual machines (VMs), leaving 30% in reserve. But once memory is exhausted, no more VMs can be installed on that server, regardless of remaining CPU or storage capacity, and the survey suggests this leads to servers being inefficiently utilized.
The lack of memory boils down to cost: Higher density modules are required to boost a machine's capacity to the levels required for virtualization (into the double-digit GB range), due to a limited number of memory sockets. But these are usually very expensive. Investing in faster or multiple processing cores, which are comparatively cheaper, is often mistakenly seen as the best way of adding capacity.
The survey was conducted by systems management vendor VKernel and was drawn from 2500 virtualized environments representing over 550,000 virtualized machines. The survey was limited to environments containing more than 50 virtual machines, so modest VM setups of just a handful of physical servers are not represented. However, the messages drawn from the data still apply.
The survey also found that, on average, each physical machine hosts 15.6 VMs, is dual-socket with quad-core processors, and contains 50GB of memory alongside 2TB of storage.
The chief benefit of virtualization is one of cost. Whereas previously each operating system required its own physical computer, virtualization allows many instances of operating systems to be installed on one physical computer. All can run simultaneously.
For example, one VM could run a company's mail server, while another could run a Web server. Yet another could provide a VPN gateway. Administrating multiple VMs is also easier than a similar setup involving multiple physical machines.
Interestingly, larger outfits with more physical machines tend to be more relaxed about capacity. Sites with 24 or more physical hosts have on average 11 VMs per physical machine, while sites with 10 or fewer machines almost double this to 20 VMs. In other words, businesses with fewer servers tend to wring more value out of them.