CASTOR: CERN's Hierarchical Storage Blueprint for Petabyte-Scale Archives

CASTOR exemplifies how hierarchical storage—combining high-speed disk with economical tape—solves the critical challenge of archiving massive scientific datasets. Its multi-tier architecture became a template for enterprise-grade solutions, demonstrating that tiered storage maximizes both performance and cost-efficiency at petabyte scale. Though CERN transitioned to CTA in 2020, CASTOR's design principles remain influential for organizations managing large-scale archives.