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Objectives of Capacity Management

          The main objective of the Capacity Management is to ensure that IT infrastructure meets business requirements today and in the future. It means that the balance between costs of infrastructure elements (hardware, software) and its efficiency/performance (available storage, time of processing data, data redundancy) should be kept. Just like the Aristotle's golden mean: the balance does not mean an equal space between the center and the borders.

Let me illustrate this on the following example: suppose your client is a bank and you are to maintain its critical IT infrastructure. Let's assume, in order to make it easier to understand, that the critical infrastructure consist of terminals that process client's online daily operations – transfers, cash withdrawals etc. There should be enough number of them in order to process data quickly even in daily peaks – at the evenings when the client's transfer is biggest. You should therefore adjust the number of terminals right to those daily peaks. Let's also assume that the proper number of terminals is 100 which is the current state. You know however that sometimes, several times a year the client's data transfer is higher than during the average daily peaks. The huge transfer is detected before the Christmas and sometimes, accidentally, in other days of the year and your research on that subject detected that in those exceptional cases the proper number of terminals is 150. So the present number of terminals you provide is not enough to maintain the performance on the average daily peak level during those super busy days and clients detect the fall of the performance then (see the picture 1. below).

Picture 1. The area above the red curve illustrates the used power of terminals - in the ideal world the number of terminals should fit perfectly to the client's generated transfer but in real life one should keep some reasonable margin (this is the black & white gradient area).
However even then there are some exceptional cases when the overall requests from client exceeds agreed limits - if you have enough budget then you should probably widen the margin hoping that the overall power would meet even exceptional demands (the green area). You should then be aware of a lot of unused space/power kept for the rest of the service time and this is your cost!.

          Here we have come to the point finally: How to resolve that problem? What to do in that enormous transfer periods: buy an additional part of terminals in order to meet client expectation anytime? But terminals are expensive and the depreciation cost is big. If you buy an additional 50 terminals the power of terminals would be unused while as we stated the number of 100 is enough. You might consider both the price of the sacrifice of that extra terminals which means client's dissatisfaction few times a year in case and the price of maintenance additional 50 terminals. Are there any alternative solutions? What is their price? This is the question for the Capacity Management and the "balance" term is so important that the separate article has been written Capcity Management – keeping balance; - I recommend you to read it to understand aspects of this word in the ITIL context.

Another important role of the Capacity Management is to estimate the growth of future requirements for IT resources. Let's come back to our example once again. Your client is keep growing and at the same time the number of it clients and the number of daily transfers increases. You as the critical IT resource and service provider should anticipate the future needs in term of month, half of the year and even longer and buy and set up the right amount of equipment in advance.

Added: 2008-09-23