Servers are no longer a "Resource Boundary"

One of the hardest concepts for System Administrators new to virtualization to understand is the shared resource management. VMware ESX makes it possible to share resources namely memory, cpu, storage and network not only inside a physical host, but also across multiple physical hosts. The resources are pulled together to create one massive resource pool captured in a concept called a cluster. Even resources inside clusters can be further subdivided into many Resource Pools. For admins who are only used to dealing with physical servers as resource boundaries this can be confusing, especially when it comes to planning and management of capacity. For example when monitoring or determining resource capacity, Admins must now take into consideration how all resource boundaries are affected. Looking just at physical servers is no longer an option!

How many new VMs are you adding per week?

How many new VMs are you adding per week? This is very important question, because it has major implication to capacity availability in your ESX data center and ultimately performance. Every VM you deploy will consume cpu, memory, storage and network resources. It will also add additional disk I/O. It is easy to see how, if uncontrolled, you can quickly run out of resources and develop capacity bottlenecks. Of course the trick is to figure out which resource you are going to run out of first? Will you hit the bottleneck in memory, cpu, storage, disk i/o or network? The answer is it really depends on your environment, but in most cases the first bottleneck is memory. Why? Remember you were able to virtualize servers, because they were under utilizing CPU. That is what enabled you to combine 8+ plus servers on one piece of hardware. When you think about memory, it is a different story. Just because your servers are now virtual, it does not mean they are consuming less memory. Hence that's why in most environments the first capacity bottleneck is memory. What do you think the second capacity bottleneck you are likely to hit? Let me know at abakman@vkernel.com