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

This note covers the following aspects: re-assessment of computing resource usage estimates for 2012 data-taking period, request of computing resource needs for 2013, and a first forecast of the 2014 needs, when restart of data-taking is foreseen. Estimates are based on 2011 experience, as well as on the results of a simulation of the computing model described in the document. Differences in the model and deviations in the estimates from previous presented results are stressed