Distributed data management on Belle II

Abstract

The Belle II experiment started taking physics data in April 2018 with an estimated total volume of all files including raw events, Monte-Carlo and skim statistics of 340 petabytes expected by the end of operations in the late-2020s. Originally designed as a fully integrated component of the BelleDIRAC production system, the Belle II distributed data management (DDM) software needs to manage data across about 29 storage elements worldwide for a collaboration of nearly 1000 physicists. By late 2018, this software required significant performance improvements to meet the requirements of physics data taking and was seriously lacking in automation. Rucio, the DDM solution created by ATLAS, was an obvious alternative but required tight integration with BelleDIRAC and a seamless yet non-trivial migration. This contribution describes the work done on both DDM options, the current status of the software running successfully in production and the problems associated with trying to balance long-term operations cost against short term risk.

Integration of Rucio in Belle II

“…The Data Management part of BelleDIRAC [7,8] provides the tools to register, read, transfer and delete files. It is integrated with the other components of BelleDIRAC and in particular the Workload Management system as shown in Fig.…”

“…Schema of the DDM system before the transition to Rucio detailing its interactions with the Workload Management of BelleDirac and the external services (catalog, storage elements, File Transfer Service). Detailed description of the system can be found in [8].…”

The Belle II Online–Offline Data Operations System

“…In addition, the BelleRawDIRAC extension makes sure that at least two copies of every raw data file are stored on the KEK and BNL permanent storage systems with at least one copy at each site. Transfer of data from KEK to BNL uses the Belle II distributed data management system [29], which is part of BelleDIRAC . As part of the plan for raw data replication development, the Distributed Data Management (DDM) engine in BelleDIRAC will be migrated to use Rucio [30,31] in the backend.…”