ISO 20000 & ITIL® Blog

ITIL Reactive and Proactive Capacity Management

Even though ITIL Capacity Management is part of Service Design, it extends across the service lifecycle. With all major service features and constraints defined within Service Strategy patterns of business activity (PBA), levels of service (LOS), and service level packages (SLPs), it’s up to Capacity Management to ensure cost-justifiable IT capacity for all current and future needs. Yes, Capacity Management is responsible for managing both current and future, with emphasis on future needs.

Before we continue, this would be a good time to read the following blog post, if you haven’t already, in order to familiarize yourself with Capacity Management basics: Three faces of Capacity Management.

Monitoring and measurement

Capacity planningFigure 1 – Capacity planning based on demand pattern

For our next example, I’ll make a safe bet that you are a smartphone user with some sort of data plan that includes a certain amount of data in your subscription. This is capacity that you have available each month for certain fee, and once you consume it all, you are left in digital darkness until the next month.

If you have no means of tracking your data usage, you are pretty much blindfolded, and can only rely on personal experience that emails generally consume a small amount of data, web browsing is a bit heavier, and photo and video sharing sites will impact your data consumption the most. It should be obvious by now that good Capacity Management strongly depends on monitoring capabilities, because what can’t be measured – can’t be controlled.

Reactive Capacity Management

Whether you measure your mobile data consumption or not, providers generally will inform you once you consume all of it (or when you spend 90% of it), but the question remains: How will you respond to that information? If that happens close to the end of the month, you’ll probably just ignore it and keep using only necessary services such as email. But, what if that happened closer to the beginning of the month?

Since you have no information about your data consumption, or you choose to ignore it, in order to continue using mobile data services you’ll have to purchase additional data for your plan. This is the perfect example of Reactive Capacity Management. When demand generated by the end-users overflows available capacity, then service degradation, or even unavailability may occur. If the business is willing to cover the costs, Capacity Management can respond in a single manner and that is to increase necessary capacity.

Proactive Capacity Management

Let’s stay with our example for a bit, and say that you have the means to monitor your data consumption. If you are commuting a lot like I do, watching videos online will have a great impact on data consumption, but how great? Luckily, my smartphone tracks how much data is consumed by every single application, and with that information I know that watching videos monthly consumes 2.9 GB, surfing the web uses 250 MB, email costs 55 MB, RSS consumes 25 MB, and all other apps combine to use 125 MB.

This totals approximately 3.35 GB of monthly data consumption, and my data plan includes only 2 GB. Does this mean that each month I purchase two additional 1 GB packages? Well, no. Initially, I did have only 2 GB, but I soon realized this consumption pattern (video, web, email, other) meant that my actual consumption was much higher. I also did some analysis on how much video I watch, the average size of mobile videos, and my web browsing patterns, and came to the conclusion that a 5 GB data plan will ensure my personal comfort for only a small increase in monthly cost.

Now that I’ve shared this information with you, I’ve come to the conclusion that I might downgrade my subscription to a plan that includes 4 GB and save a few Euros. Now that’s Proactive Capacity Management I like.

Fine tune

As shown in Figure 1, successful Capacity Management will have Service Process perfectly matched with Business Process, as if they were two wheels connected with a belt.  In reality, you’ll probably never have such a case, and that is why we need control mechanisms; we can either try to control demand via Demand Management, or simply react to demand via Capacity Management.

The best practice suggests that both methods should be used in conjunction, but in a very controlled fashion, which is illustrated in Figure 1 with blue and orange circular arrows. Imagine what the end result would look like, if Demand and Capacity Management ran independently; on increased load, Demand Management would react with the goal to reduce it, while Capacity Management would increase available capacity…

Reactive Capacity Management is important for a swift response in increasing demand, which can’t be offloaded by Demand Management (e.g., increase in number of employees), while Proactive Capacity management is reliant on monitoring and measuring capabilities, trend analysis, and similar methods to predict, fine-tune and restore the balance between all the components in the service belt.

Good Capacity Management starts with a Capacity Plan, so I’d like to use this opportunity to suggest the following article, which describes all the elements of an ITIL Capacity Plan – A document you need, but probably don’t have.

To get a better overview of your Capacity Management process, use this free  ITIL Gap Analysis Tool.