Server consolidation has become an integral part of IT planning to reduce cost and improve efficiency in today's enterprise datacenters. The advent of resource virtualization allows consolidation of multiple applications into virtual servers hosted on a single or multiple physical servers. However, despite its salient features, this poses new challenges, including selection of the right virtualization technology and consolidation configuration for a particular set of applications. In this paper, we evaluate two representative virtualization technologies, Xen and OpenVZ, in various configurations. We consolidate one or more multi-tiered systems onto one or two nodes and drive the system with an auction workload called RUBiS. We compare both technologies with a base system in terms of application performance, resource consumption, scalability, low-level system metrics like cache misses, and virtualization-specific metrics like Domain-0 consumption in Xen. Our experiments indicate that the average response time can increase by more than 400% in Xen and by a more modest 100% in OpenVZ as the number of application instances grows from one to four. This large discrepancy is found to come from the higher virtualization overhead in Xen, which is likely caused by higher L2 cache misses and larger number of misses per instruction. A similar trend is observed in the CPU consumptions of the virtual servers.We analyze the overhead with kernel-symbol-specific information generated by Op rofile and suggest possible remedies for these problems. 13 Pages
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