Abstract

The Simulation at Point1 (Sim@P1) project was established in 2013 to take advantage of the Trigger and Data Acquisition High Level Trigger (HLT) farm of the ATLAS experiment at the LHC. The HLT farm is a significant compute resource, which is critical to ATLAS during data taking. This large compute resource is used to generate and process simulation data for the experiment when ATLAS is not recording data. The Sim@P1 system uses virtual machines, deployed by OpenStack, in order to isolate the resources from the ATLAS technical and control network. During the upcoming long shutdown in 2019 (LS2), the HLT farm including the Sim@P1 infrastructure will be upgraded. A previous paper on the project emphasized the need for “simple, reliable, and efficient tools” to quickly switch between data acquisition operation and offline processing. In this contribution we assess various options for updating and simplifying the provisional tools. Cloudscheduler is a tool for provisioning cloud resources for batch computing that has been managing cloud resources in HEP offline computing since 2012. We present the argument for choosing Cloudscheduler, and describe technical details regarding optimal utilization of the Sim@P1 re-sources.

Highlights

  • ATLAS [1] is a general purpose experiment located at point one (P1) of CERN’s large hadron collider

  • The High Level Trigger (HLT) was switched from Trigger and Data Acquisition (TDAQ) function to Simulation at Point1 (Sim@P1) mode for intervals of a few days during technical stops and machine development

  • When the opportunistic resources of the HLT are switched to Sim@P1 mode, the farm is one of the largest resources for ATLAS offline computing

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Summary

Introduction

ATLAS [1] is a general purpose experiment located at point one (P1) of CERN’s large hadron collider. The virtual machines share the “data” connection of the HLT hardware through a tagged VLAN providing network isolation on the level of the Ethernet frame managed by the switches. This VLAN allows the Virtual Machines to connect to a controlled list of interfaces in the CERN general purpose network. The HLT was switched from TDAQ function to Sim@P1 mode for intervals of a few days during technical stops and machine development To allow this opportunistic usage a set of scripts were developed to manage the transition of resources between TDAQ and Sim@P1 mode. Should reconstruction workflows be allowed on Sim@P1 in the future, as discussed this configuration will need to be re-examined

Operational experience
Simulation
Reconstruction and derivation
Event generation
Cloudscheduler
Vacuum
Libvirt
Containers
Summary
Full Text
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