How to Manage Capacity in Virtualized Environments

Virtualization introduces a new capacity management paradigm, forcing IT administrators to reassess how they currently plan and manage data center capacity. Here, Knowledge Center contributor Rob Smoot discusses various capacity management methods, explaining why capacity management is important, and how it differs in the physical world versus a virtualized one.


With virtualization, data center resources are shared in an adaptive, large communal pool of dynamic capacity. Because capacity is shared, there is a ripple effect in the data center cluster; when one application or virtual machine zigs, others must zag in response since capacity is finite. As a result, capacity planning and management is a higher stakes game in a virtual environment. IT shops need tools that intimately understand this dynamic new layer and can help ensure that adequate capacity is on hand when it's needed.

So, what exactly is capacity management? Let's start with some level-setting definitions. According to the Information Technology Infrastructure Library (ITIL), capacity management is the discipline that ensures IT infrastructure is used in the most efficient, predictable and cost-effective manner. In basic economic terms, it's about balancing business demand with IT supply. All organizations practice capacity planning and management in some shape or form. It may not be as structured or programmatic as ITIL, but certainly the need is there and, fundamentally, we all do it to some degree.

To be clear, capacity management is not just simply about ensuring enough IT capacity for the business. That part is very easy to do; anyone can guarantee enough capacity if you just over-purchase or over-provision your capacity. The key goals are efficiency and predictability.

It's about finding the optimal balance of IT supply to meet the business demands at all times. It's about reducing costs while minimizing waste and risk. As a result, effective capacity management ensures two things:

1. Efficiency (optimization of capacity): using every last bit of available capacity, without impacting the business.

2. Predictability (availability of capacity): ensuring capacity is always available and always on, whenever the business needs it.