Design and Performance of ATLAS Tier 3 Computing Facility Based on Virtual Machine Technology

We have developed an ATLAS Tier 3 computing facility based on Virtual Machine (VM) technology. In our system all worker nodes are CernVM based virtual machines running on a SUSE Xen hypervisor. Utilization of VM technology in a Tier 3 farm allows one to simplify not only system configuration and management, but also experiment specific software installation and configuration. That in turn reduces manpower required to run such a facility which is an important factor in the Tier 3 context. We have explored performance of a virtualized Tier 3 facility on a variety of workloads typical for the ATLAS. We have found that the performance of typical ATLAS workloads in the virtualized environment was adequate, with an acceptable performance penalty from virtualization in most scenarios. We've also found cases where jobs running in VM were faster than the ones running in a physical machine.