Your cloud may not be a cloud. Private cloud computing goes beyond rebranding virtualisation. Virtualisation is an enabling technology, but public cloud applications are attractive because of their flexibility and pay-as-you-go nature. What are you doing to bring those characteristics within your firewall? If your infrastructure is virtual, but you're managing virtual machines the same way you've always managed servers, maybe your cloud isn't really a cloud.

You must be able to respond to fluctuating capacity needs. Your private cloud should provide for rapid provisioning and re-provisioning of capacity. Public cloud services accomplish this with large server farms. Within a corporate network, you won't be able to justify having thousands of servers sitting idle, but you should have a way of quickly ­reallocating the capacity you have when user needs demand it.

You need chargeback mechanisms. You should be able to measure and charge for use of cloud servers and services. With cloud services, you only pay for what you use, and you pay more when you use more. Firms that lack a strong central services organisation with chargeback mechanisms are likely to be organisationally incapable of implementing a fair chargeback system, says Brad Tagg, a cloud consultant and former IBM Distinguished Engineer.

You must decide who controls access, you or the users. You will have to decide where to draw the line with self-provisioning versus centralised control. Anyone with a credit card can sign up for an account on a public cloud service in a matter of minutes. What would the equivalent look like within your organisation? Do you want employees or departments provisioning their own user accounts, or assigning themselves big blocks of storage?

Now's the time to plan for future options. How you architect your private cloud affects how you expand. For example, some service providers are adopting VMware standards while Amazon Web Services use open source Xen virtualisation technology. Kevin Smilie, a partner at the consulting firm TPI, says establishing the right service management discipline will put you in a better position "when you need a burst of capability beyond your own firewall."