INFN Tier-1 experiences with Castor-2 in CMS computing challenges

The CMS combined Computing, Software and Analysis challenge of 2006 (CSA06) is a 50 million event exercise to test the workflow and dataflow associated with the data handling model of CMS. It was designed to be a fully Grid-enabled, 25% capacity exercise of what is needed for CMS operations in 2008. All CMS Tier1’s participated, and the INFN Tier-1 - located at CNAF, Bologna, Italy - joined with a production Castor-2 installation as a Hierarchical Storage Manager solution to address data storage, dat access and custodial responsibility. After the prompt reconstruction phase at the Tier-0, the data was distributed to all participating Tier-1’s, and calibration/alignment, re-reconstruction and skimming jobs ran at the Tier-1’s. Output of skimming jobs were propagated to the Tier-2’s, to allow physics analysis job submissions. The experience collected by the INFN Tier-1 storage group during the pre-challenge Monte Carlo production, the preparation and the running of the CSA06 exercise - as well as the Tier-1 preparation activities for next CMS Computing challenges in 2007 - are reviewed and discussed.