  It is widely accepted that cosmic rays are a plausible cause of DRAM errors
in high-performance computing (HPC) systems, and various studies suggest that
they could explain some aspects of the observed DRAM error behavior. However,
this phenomenon is insufficiently studied in production environments. We
analyze the correlations between cosmic rays and DRAM errors on two HPC
clusters: a production supercomputer with server-class DDR3-1600 and a
prototype with LPDDR3-1600 and no hardware error correction. Our error logs
cover 2000 billion MB-hours for the MareNostrum 3 supercomputer and 135 million
MB-hours for the Mont-Blanc prototype. Our analysis combines quantitative
analysis, formal statistical methods and machine learning. We detect no
indications that cosmic rays have any influence on the DRAM errors. To
understand whether the findings are specific to systems under study, located at
100 meters above the sea level, the analysis should be repeated on other HPC
clusters, especially the ones located on higher altitudes. Also, analysis can
(and should) be applied to revisit and extend numerous previous studies which
use cosmic rays as a hypothetical explanation for some aspects of the observed
DRAM error behaviors.
