Performance Tests of CMSSW on the CernVM

The CERN Virtual Machine (CernVM) Software Appliance is a project developed in CERN with the goal of allowing the execution of the experiment's software on different operating systems in an easy way for the users. To achieve this it makes use of Virtual Machine images consisting of a JEOS (Just Enough Operational System) Linux image, bundled with CVMFS, a distributed file system for software. This image can this be run with a proper virtualizer on most of the platforms available. It also aggressively caches data on the local user's machine so that it can operate disconnected from the network. CMS wanted to compare the performance of the CMS Software running in the virtualized environment with the same software running on a native Linux box. To answer this need a series of tests were made on a controlled environment during 2010-2011. This work presents the results of those tests.