Controlling a Large CPU Farm Using Industrial Tools

The LHCb experiment at CERN will have an Event Filter Farm (EFF) composed of 2000 CPUs. These machines will form a pool of 50 sub-farms with 30 to 40 nodes each, running a large amount of High Level Trigger (HLT) tasks in parallel. Although these tasks are identical algorithms, they can run at the same time being configured with different parameters, such as run type (Physics, Cosmics, Test, etc), HLT rate or with different subdetectors (partitions). The HLT is the second of the two trigger levels in LHCb. Its selection algorithms reduce the incoming data rate of 1 MHz to an output rate of 2 kHz. Selected events are sent for mass storage and subsequent offline reconstruction and analysis. These trigger processes running online are based on the same software framework as the algorithms for offline analysis (Gaudi). The control of the trigger farm was developed with an industrial SCADA system (PVSS) which is used throughout the Experiment Control System (ECS). The HLT algorithms are handled by the ECS like hardware devices, for instance, high voltage channels. The integration of the HLT controls in the overall ECS, which is modeled as finite state machines, will be presented.