Data centres and other infrastructures in the field of information technology suffer from the major issue of ‘server sprawl’, a term used to depict the situation wherein a number of servers consume resources inefficiently, when compared to the business value of outcome obtained from them. Consolidation of servers, rather than dedicating whole servers to individual applications, optimizes the usage of hardware resources, and virtualization achieves this by allowing multiple servers to share a single hardware platform. Server virtualization is facilitated by the usage of hypervisors, among which Xen is widely preferred because of its dual virtualization modes, virtual machine migration support and scalability. This research work involves an analysis of the CPU scheduling algorithms incorporated into Xen, on the basis of the algorithm’s performance in different workload scenarios. In addition to performance evaluation, the results obtained lay emphasis on the importance of compute intensive or I/O intensive domain handling capacity of a hypervisor’s CPU scheduling algorithm in virtualized server environments. Based on this knowledge, the selection of CPU scheduler in a hypervisor can be aligned with the requirements of the hosted applications. A new credit-based VCPU scheduling scheme is proposed, in which the credits remaining for each VCPU after every accounting period plays a significant role in the scheduling decision. The proposed scheduling strategy allows those VCPUs of I/O intensive domains to supersede others, in order to favour the reduction of I/O bound domain response times and the subsequent bottleneck in the CPU run queue. Though a small percentage of context switch overhead is introduced, the results indicate substantial improvement of I/O handling and fairness in re-source allocation between the host and guest domains.

Abstract This thesis deals with the process of server consolidation, which is tightly connected to IT infrastructure of virtually any organization. Moreover it is dealt in some respect with the way the organization runs and with linking these two particular areas together. The goal of this thesis is to identify consequences or impacts of server consolidation process on the way the organization functions and on methods how to measure these impacts. One of the steps towards this goal is unmistakably analyzing the planning and deployment of server consolidation including virtualization technology. Server consolidation is characterized as a process leading to simplified and more effective IT infrastructure of an organization. To analyze the IT infrastructure in complete and systematic way it is used framework called IT Infrastructure Library respectively part of it called ICT Infrastructure Management. Because of that linking of the server consolidation process progress to organization's global goals is granted. Contribution of this thesis can be seen in complex analysis of the consequences of the server consolidation process to the functioning of an organization. Especially in areas that are usually not being considered in connection with server consolidation, which is considered to be IT matter, such as human resources and social enviroment. Key words: server consolidation, server consolidation consequences, ICT Infrastructure Management, Virtualization

The goal of the thesis is to examine and assess actual portfolio of products on the market for server visualization and to compare performance of individual products with performance of the physical machine. The research and the assessment of the actual portfolio will be carried out with the focus on current trends in the area of server virtualization, reasons for realization, and important aspects for their successful implementation. The comparison will be carried out in areas of supported platforms, hardware emulation spectra, hardware limitations, licensing and prices. Further it will be performed comparison in the form of benchmark performance in areas of CPU, RAM, hard-drive throughput, and network throughput of most commonly used products for server virtualization.

The thesis aims on a proposal of server infrastructure utilization within a particular organization based on a virtual environment. Analysis of current company’s IT infrastructure was chosen as a starting point for subsequent draft of suitable server consolidation solution that includes all necessary aspects from server configuration up to virtual environment conversion itself. Price calculation and benefits of proposed solution are listed at the end of the thesis.

Based on an application in the field of server consolidation, we consider the one-dimensional cutting stock problem with nondeterministic item lengths. After a short introduction to the general topic we investigate the case of normally distributed item lengths in more detail. Within this framework, we present two lower bounds as well as two heuristics to obtain upper bounds, where the latter are either based on a related (ordinary) cutting stock problem or an adaptation of the first fit decreasing heuristic to the given stochastical context. For these approximation techniques, dominance relations are discussed, and theoretical performance results are stated. As a main contribution, we develop a characterization of feasible patterns by means of one linear and one quadratic inequality. Based on this, we derive two exact modeling approaches for the nondeterministic cutting stock problem, and provide results of numerical simulations.