System designHardsd-g723

Subject Block storageLevel Senior–Staff~40 minCommon in Storage & CDN interviewsIndustries Technology

Question

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?

What a strong answer looks like

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.

Learn the concepts

Narrate your design

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Run or narrate your approach, then ask the coach.