Impact of RNTuple on Storage Resources for ATLAS Production

Over the past years, the ROOT team has been developing a new I/O format called RNTuple to store data from experiments at CERN’s Large Hadron Collider. RNTuple is designed to improve ROOT’s existing TTree I/O subsystem by improving I/O speed and introducing a more efficient binary data format. It can be stored in both ROOT files and object stores, and it is optimized for modern storage hardware like NVMe SSDs. The ATLAS experiment plans to use RNTuple as its primary storage container in the upcoming High Luminosity-LHC (HL-LHC) data taking. There has been significant progress in integrating RNTuple into the ATLAS event processing framework, and now all production ATLAS data output formats support it. Performance studies with open-source data have shown substantial improvements in space resource usage. The reported study examines the I/O throughput and disk-space savings achieved with RNTuple for various ATLAS data output formats. These measurements will have an important impact on the computing resource needs of the ATLAS experiment for HL-LHC operation.