Tiered storage with hot/cold placement

Design a hybrid local-storage tier for database hosts that places hot data on fast NVMe SSD and colder data on cheaper, larger media, presenting a single logical volume. The DB does mixed random reads and bursty writes; you must keep p99 read latency low for the working set while controlling cost, and avoid write cliffs when the SSD cache fills. How do you decide what's hot, place data, and schedule I/O?