System Design Card 389 — Storage Choice / Implement
Concern
Storage determines consistency, latency, indexing flexibility, and operational complexity. Key-value storage may suit a short-link lookup, while relational or search-oriented systems may fit different query patterns.
What Implement means for this concern
In BASIC, the Implement step is where you walk the design into existence in a controlled order, deepening the risky parts first. For Storage Choice, that means the candidate should make this concern visible at the right moment instead of bolting it on at the end.
Design move
A good move is to transcribe the plan instead of improvising. Tie the concern back to the user flow, the workload, and the dominant trade-off. That keeps the design grounded and makes it easier for the interviewer to follow why a cache, queue, replica, partition, or rate limiter is actually necessary.
Common miss
Candidates often choose a database by brand name rather than by access pattern. BASIC helps because the staged flow keeps this concern proportional to the prompt and connected to the rest of the architecture.
BASIC prompt
“When I reach the Implement stage, how does Storage Choice change the architecture, the trade-offs, or the review checklist?”