Benjamin Ambrož (2010) Zmogljivostna analiza strežnika za nudenje storitve video na zahtevo. EngD thesis.
With the development of information and communication technologies, video-on-demand services have become widely used, what is more, they have also become a part of regular offer of IPTV. Video-on-demand represents the peak of multimedia and it requires capable computers for its functioning – video servers and especially adjusted operating systems which support handling multimedia in the way that it can meet the user’s requirements for watching video content. The theoretical part of the thesis introduces algorithms which are used by multimedia operating systems for process scheduling, block and file caching, disk scheduling and placing movie files on disks. The emphasis is on the file placement since the aim of the empirical part of the thesis has been to construct a simulation model of the load balanced disk subsystem of the VOD server. Due to the varying popularity of movies between the users and consequently the significant asymmetry in access demand, can the file assignment problem, in order to achieve minimum request blocking probability, be considered as nontrivial. For a heuristic solution of the NP-complete problem we have used a greedy file allocation method that realizes an efficient localized file placement scheme with non-uniform replication strategy – the combination load balancing scheme (CLB). The discrete event simulation study of CLB with the performance analysis has been done with the help of simulation tool Simprocess. By conducting experiments we have gained a better insight into the functioning of the disk subsystem of the VOD server at different configurations. Furthermore, we have checked the efficiency of two exhaustive resource selection schemes which are used by the CLB scheme, i.e. repeated random trials (RRT) and least busy fit (LBF). The latter has proved itself as more effective. The results of the experiments have also confirmed that a greedy file allocation method decides a good quality heuristic solution for each feasible file replication instance. The simulation model can be applied to the design of a large-scale and load balanced disk subsystem of the VOD server and for its tuning. In the conclusion we have devised how to get approximate results faster with an analytical method.
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