E. Dénes

DDL, the ALICE data transmission protocol and its evolution from 2 to 6 Gb/s

ALICE (A Large Ion Collider Experiment) is the detector system at the LHC (Large Hadron Collider) that studies the behaviour of strongly interacting matter and the quark gluon plasma. The information sent by the sub-detectors composing ALICE are read out by DATE (Data Acquisition and Test Environment), the ALICE data acquisition software, using hundreds of multi-mode optical links called DDL (Detector Data Link). To cope with the higher luminosity of the LHC, the bandwidth of the DDL links will be upgraded in 2015. This paper will describe the evolution of the DDL protocol from 2 to 6 Gbit/s.

PCI Based Read-out Receiver Card in the ALICE DAQ System

The PCI-based Readout Receiver Card (PRORC) is the primary interface between the detector data link (an optical device called DDL) and the front-end computers (PC running Linux) of the ALICE data acquisition system. This document describes the prototype architecture of the PRORC hardware and firmware, and of the PC software. The board contains a PCI interface circuit and an FPGA. The firmware in the FPGA is responsible for all the concurrent activities of the board, such as reading the DDL and controlling the DMA. The co-operation between the firmware and the PC software allows autonomous data transfer into the PC memory with little CPU assistance. The system achieves a sustained transfer rate of 100 MB/s, meeting the design specifications and the ALICE requirements.

The ALICE Data-Acquisition Read-out Receiver card

The ALICE data-acquisition system will use more than 400 optical links, called Detector Data Links (DDLs) to transfer the data from the detector electronics directly into the PC memory through a PCI adapter: the DAQ Read-out Receiver Card (D-RORC). The D-RORC includes two DDL interfaces, which can either receive detector data, or copy and transfer them to the High-Level Trigger system. Using the 64-bit PCI interface IP core, the D-RORC offers more than 400 MB/s bandwidth. This document describes the hardware and firmware architecture, the co-operation with the software running on the PC, as well as the performance of the D-RORC.

The ALICE DAQ: current status and future challenges

The ALICE data acquisition system has been designed to support an aggregate event-building bandwidth of up to 2.5 GByte/s and a storage capability of up to 1.25 GByte/s to mass storage. A general framework called the ALICE Data Acquisition Test Environment (DATE) system has been developed as a basis for prototyping the components of the DAQ. DATE supports a wide spectrum of configurations from simple systems to more complex systems with multiple detectors and multiple event builders. Prototypes of several key components of the ALICE DAQ have been developed and integrated with the DATE system such as the ALICE Detector Data Link, the online data monitoring from ROOT and the interface to the mass storage systems. Combined tests of several of these components are being pursued during the ALICE Data Challenges. The architecture of the ALICE DAQ system will be presented together with the current status of the different prototypes. The recent addition of a Transition Radiation Detector (TRD) to ALICE has required a revision of the requirements and the architecture of the DAQ. This will allow for a higher level of data selection. These new opportunities and implementation challenges will also be presented.

System performance monitoring of the ALICE Data Acquisition System with Zabbix

ALICE (A Large Ion Collider Experiment) is a heavy-ion detector studying the physics of strongly interacting matter and the quark-gluon plasma at the CERN LHC (Large Hadron Collider). The ALICE Data-AcQuisition (DAQ) system handles the data flow from the sub-detector electronics to the permanent data storage in the CERN computing center. The DAQ farm consists of about 1000 devices of many different types ranging from direct accessible machines to storage arrays and custom optical links. The system performance monitoring tool used during the LHC run 1 will be replaced by a new tool for run 2. This paper shows the results of an evaluation that has been conducted on six publicly available monitoring tools. The evaluation has been carried out by taking into account selection criteria such as scalability, flexibility, reliability as well as data collection methods and display. All the tools have been prototyped and evaluated according to those criteria. We will describe the considerations that have led to the selection of the Zabbix monitoring tool for the DAQ farm. The results of the tests conducted in the ALICE DAQ laboratory will be presented. In addition, the deployment of the software on the DAQ machines in terms of metrics collected and data collection methods will be described. We will illustrate how remote nodes are monitored with Zabbix by using SNMP-based agents and how DAQ specific metrics are retrieved and displayed. We will also show how the monitoring information is accessed and made available via the graphical user interface and how Zabbix communicates with the other DAQ online systems for notification and reporting.

O2: A novel combined online and offline computing system for the ALICE Experiment after 2018

ALICE (A Large Ion Collider Experiment) is a detector dedicated to the studies with heavy ion collisions exploring the physics of strongly interacting nuclear matter and the quark-gluon plasma at the CERN LHC (Large Hadron Collider). After the second long shutdown of the LHC, the ALICE Experiment will be upgraded to make high precision measurements of rare probes at low pT, which cannot be selected with a trigger, and therefore require a very large sample of events recorded on tape. The online computing system will be completely redesigned to address the major challenge of sampling the full 50 kHz Pb-Pb interaction rate increasing the present limit by a factor of 100. This upgrade will also include the continuous un-triggered read-out of two detectors: ITS (Inner Tracking System) and TPC (Time Projection Chamber)) producing a sustained throughput of 1 TB/s. This unprecedented data rate will be reduced by adopting an entirely new strategy where calibration and reconstruction are performed online, and only the reconstruction results are stored while the raw data are discarded. This system, already demonstrated in production on the TPC data since 2011, will be optimized for the online usage of reconstruction algorithms. This implies much tighter coupling between online and offline computing systems. An R&D program has been set up to meet this huge challenge. The object of this paper is to present this program and its first results.

Preparing the ALICE DAQ upgrade

In November 2009, after 15 years of design and installation, the ALICE experiment started to detect and record the first collisions produced by the LHC. It has been collecting hundreds of millions of events ever since with both proton and heavy ion collisions. The future scientific programme of ALICE has been refined following the first year of data taking. The physics targeted beyond 2018 will be the study of rare signals. Several detectors will be upgraded, modified, or replaced to prepare ALICE for future physics challenges. An upgrade of the triggering and readout systems is also required to accommodate the needs of the upgraded ALICE and to better select the data of the rare physics channels. The ALICE upgrade will have major implications in the detector electronics and controls, data acquisition, event triggering and offline computing and storage systems. Moreover, the experience accumulated during more than two years of operation has also lead to new requirements for the control software. We will review all these new needs and the current R&D activities to address them. Several papers of the same conference present in more details some elements of the ALICE online system.

Orthos, an alarm system for the ALICE DAQ operations

ALICE (A Large Ion Collider Experiment) is the heavy-ion detector studying the physics of strongly interacting matter and the quark-gluon plasma at the CERN LHC (Large Hadron Collider). The DAQ (Data Acquisition System) facilities handle the data flow from the detectors electronics up to the mass storage. The DAQ system is based on a large farm of commodity hardware consisting of more than 600 devices (Linux PCs, storage, network switches), and controls hundreds of distributed hardware and software components interacting together. This paper presents Orthos, the alarm system used to detect, log, report, and follow-up abnormal situations on the DAQ machines at the experimental area. The main objective of this package is to integrate alarm detection and notification mechanisms with a full-featured issues tracker, in order to prioritize, assign, and fix system failures optimally. This tool relies on a database repository with a logic engine, SQL interfaces to inject or query metrics, and dynamic web pages for user interaction. We describe the system architecture, the technologies used for the implementation, and the integration with existing monitoring tools.

The ALICE DAQ, current status and future evolution

ALICE (A Large Ion Collider Experiment) is the heavy-ion detector designed to study the physics of strongly interacting matter and the Quark-Gluon Plasma at the CERN Large Hadron Collider (LHC). A large bandwidth and flexible Data-Acquisition System (DAQ) has been designed and deployed to collect sufficient statistics in the short running time available per year for heavy ions and to accommodate very different requirements originating from the 18 sub-detectors. After several months of data taking with beam, lots of experience has been accumulated and some important developments have been initiated in order to evolve towards a more automated and reliable experiment. We will present the experience accumulated so far and the new developments. Several upgrades of existing ALICE detectors or addition of new ones have also been proposed with a significant impact on the DAQ. We will review these proposals, their implication for the DAQ and the way they will be addressed.

Radiation Tolerance Qualification Tests of the Final Source Interface Unit for the ALICE Experiment

The ALICE Detector Data Link (DDL) is a high-speed optical link designed to interface the readout electronics of ALICE sub-detectors to the DAQ computers. The Source Interface Unit (SIU) of the DDL ...