Buffering Strategies for Large-Scale Data-Acquisition Systems

Data acquisition systems for particle physics experiments produce vasts amounts of data. It is sometimes unfeasible to store it all since the storage requirements will be enormous. For this reason, an on-line filtering system selects the relevant pieces of information according to the goals of the experiment, before finally sending them to permanent storage. While data is being analyzed, it is temporarily stored in a large high-speed buffering system. Data production follows a cycle, with long periods of many hours where no data is being produced by the experiment. Also, data production is not constant, and there are fluctuations in the input rate. This offers the possibility of over-provisioning the buffering system and trading processing power for storage space. This buffer can be used for storage for periods of many days. In this work, a model was created to study the behavior of some aspects of the ATLAS data acquisition system, and specifically the buffering system for the on-line filter.