The Alice O2 Event Processing Nodes (EPNs) consists of 250 servers, each with 2 AMD Rome 32 core CPUs, 512 GB RAM, 8 AMD MI50 GPUs with 32GB memory each, as well as an Infiniband HDR network interface. The main purpose and the driving design factors of the cluster are the real-time online reconstruction capabilities during Alice Pb-Pb data taking. The EPNs get up to 635 GB/s of zero suppressed detector data as input. Most of this data comes from the Time Projection Chamber (TPC). The EPNs use General Purpose Graphics Processing Units (GPGPUs) to do a full reconstruction of the data, to get the total data size down to ca. 100 GB/s, so it can be stored in our disk buffer. While the experiment is not taking data, the cluster is used as an analysis facility, reading the data from the disk buffer for additional processing and physics analysis.
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