Abstract
The ALICE experiment at CERN LHC (Large Hadron Collider) is undertaking a major upgrade during LHC Long Shutdown 2 in 2019-2020. The raw data input from the detector will then increase a hundredfold, up to 3.4 TB/s. In order to cope with such a large throughput, a new Online-Offline com-9 puting system, called O2, will be deployed. The FLP servers (First Layer Pro-10 cessor) are the readout nodes hosting the CRU (Common Readout Unit) cards in charge of transferring the data from the detector links to the computer mem-12 ory. The data then flow through a chain of software components until they are shipped over network to the processing nodes. In order to select a suitable plat-14 form for the FLP (First Level Processor), it is essential that the hardware and the software are tested together. Each candidate server is therefore equipped with multiple readout cards (CRU), one InfiniBand 100G Host Channel Adapter, and the O2 readout software suite. A series of tests are then run to ensure the readout system is stable and fulfils the data throughput requirement of 42Gbps (highest data rate in output of the FLP equipped with three CRUs). This paper presents the software and firmware features developed to evaluate and validate different candidates for the FLP servers. In particular we describe the data flow from the CRU firmware generating data, up to the network card where the buffers are sent over the network using RDMA. We also discuss the testing procedure and the results collected on different servers.
Highlights
The ALICE[1] experiment at CERN LHC (Large Hadron Collider) is undertaking a major upgrade during LHC Long Shutdown 2 in 2019-2020
In order to cope with the high data throughput expected by the detector, 3.4 TB/s, a new data acquisition farm has been designed
A series of tests were carried out to verify the correct behavior of the server equipped with multiple readout cards, up to a maximum of three
Summary
The ALICE[1] experiment at CERN LHC (Large Hadron Collider) is undertaking a major upgrade during LHC Long Shutdown 2 in 2019-2020. Different candidates have been identified as possible readout server. The readout requirements for RUN3 are very demanding and the server must be able to handle high data throughput up to a maximum of 100 Gbps (input and output) for long periods of data taking. A series of tests were carried out to verify the correct behavior of the server equipped with multiple readout cards, up to a maximum of three. In order to be selected, the candidate server had to satisfy various hardware and software criteria. Mechanical installation, heat dissipation, BIOS settings and memory installation are only a few requirements that defined the selection procedure for the readout server. Dedicated software and firmware have been written to test different FLP candidates and to decide the best one for ALICE requirements.
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