Tiered storage hot-cold migration
Design the tiered-storage layer for a database/analytics engine whose dataset (500TB and growing) far exceeds what fits on local SSD, but 95% of queries touch data from the last 30 days. You want recent/hot data on fast local NVMe and old/cold data on cheap object storage (S3-class), with migration happening automatically as data ages, and queries that occasionally reach into cold data must still work — just slower. Design how data is placed across tiers, how it migrates hot->cold (and back if it gets hot again), how a query transparently reads across tiers, and the trade-off you're managing.
Clarify scale and constraints first. Propose a clean component breakdown, then go deep on the hard parts (data model, bottlenecks, consistency, failure modes) and name the trade-offs you are making.