LHCb Computing Resources: 2012, 2013 re-assessment and 2014 request

This document presents an update of the computing resource estimates for LHCb. It presents a re-evaluation of the 2012-13 requirements in view of the updated LHC schedule, and the new request for 2014. This document should be considered an update of LHCb-PUB-2011-009, in which 2012 resource requests were initially presented, and LHCb-PUB-2012-004, where the estimates were updated in view of the 2011 experience. The model presented will follow the nominal LHCb computing model, in which all real-data processing activities take place at the Tier0/1s while the Monte Carlo simulation is taken care of by Tier2s and any other computing resources to which we can get access. When necessary these roles can be mixed to dedicate larger amounts of CPU power to any of these main activities. Differences in the model and deviations from previous estimates are described