High-speed data-injection for data-flow verification at LHCb

Abstract

The High Level Trigger (HLT) and Data Acquisition System select about 2 kHz of events out of the 40 MHz of beam crossings. The selected events are consolidated into files on an onsite storage and then sent to permanent storage for subsequent analysis on the Grid. For local and full-chain tests a method to exercise the data-flow through the HLT when there are no actual data needed. In order to test the system as much as possible under identical conditions as for data-taking the solution would be to inject data at the input of the HLT at a minimum rate of 2 kHz. This is done via a software implementation of the trigger system which sends data to the HLT. The application has to simulate that the data it sends come from a real LHCb readout-boards. Data can come from several input streams, which are selected according to probabilities or frequencies. Therefore the emulator offers runs which are more than identical data-flows coming from a sequence on tape, but physics-like pseudo-indeterministic data-flow, including lumi events and likely interesting b-quark events. Both simulation data and previously recorded real data can be re-played through the system in this manner. As the data rate is high (100 MB/s), care has been taken to optimize the emulator for throughput from the Storage Area Network. The emulator can be run in stand-alone mode but is even more interesting that it can emulate any partition of LHCb in parallel with the real hardware partition. In this mode it is fully integrated into the standard run-control. The architecture, implementation, and performance results of the emulator and full tests will be presented. This emulator is a key piece in the ongoing data-challenges in LHCb. Results from these Full System Integration Tests (FEST) will be presented, which helped to verify and benchmark the entire LHCb data-flow.