Storage Layer Monitoring data is stored in a time-series database optimised for the analytical queries PMM requires: aggregation over time windows, comparison between periods, and disaggregation by subgroup. For high-volume systems, a tiered storage strategy reduces cost: raw inference data is retained at full granularity for a defined period (typically 30–90 days), then aggregated to hourly or daily summaries for long-term retention. The Technical SME documents the aggregation methodology in the PMM plan. The raw data retention period must be sufficient to support serious incident investigations; a serious incident discovered weeks after it occurred requires access to the raw data from the incident period. Long-term storage uses the same tiered approach as the broader evidence repository : active storage for current data, archival storage (S3 Glacier, Azure Archive, Google Archive) for historical data, with lifecycle policies enforcing the ten-year retention period. Key outputs

• Time-series database optimised for PMM queries
• Tiered storage (raw 30–90 days, aggregated long-term)
• Raw data retention sufficient for incident investigation
• Ten-year archival with lifecycle policies