Abstract. In this paper we propose a communication relay scheme combining the NAT and a user-level proxy to support private IP clusters in Grid environments. Compared with the user-level two-proxy scheme used in PACX-MPI and Firewall-enabled MPICH-G, the proposed scheme shows performance improvement in terms of latency and bandwidth between the nodes located in two private IP clusters. Since the proposed scheme is portable and provides high performance, it can be easily applied to any private IP enabled solutions including the private IP enabled MPICH solution for Globus toolkit.

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Managing hardware resources efficiently when they are shared in virtualized environment is a critical issue for improving application QoS. For CPU resources, virtual machine scheduling delays should be additionally concerned, because they cause unexpected service delays to guest applications and can consequently violate the application QoS. There have been many researches to manage CPU resources by monitoring resource utilization and analyzing application performance via mathematical techniques such as queuing models. However, most of the studies cannot always guarantee the application QoS, because they do not reflect the virtual machine scheduling delay. In this paper, we propose a CPU provision scheme considering virtual machine scheduling delays in Xen environment. We compare the performance of the proposed scheme with that of Sandpiper and show that the proposed scheme decreases the number of SLA violations.

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