Your question is Metrics Storage Without Losing History. Take a moment with it on the right.
Talk me through your thinking if you like. When you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes).
(Scenario) If a monitoring system is collecting metrics every 10 seconds from multiple systems and writing the metrics data to a DB, and the DB disk is getting full frequently, how would you solve it without increasing DB disk space or removing the last 6 months of metrics history?