An Infrastructure-as-a-Service (IaaS) provider is usually assumed to own a large data centre with significant computational resources. For a small or medium sized Internet Data Centre (IDC), offering cloud computing service is a nature of business model but there are technical barriers which need to be resolved. One of the key issues is ineffective resource management given such an IDC usually has only limited resource. In this paper, we propose an efficient resource management solution specially designed for helping small and medium sized IaaS cloud providers to better utilise their hardware resources with minimum operational cost. Such an optimised resource utilisation is achieved by a well-designed underlying hardware infrastructure, an efficient resource scheduling algorithm and a set of migrating operations of VMs.