NALSD (Non-Abstract Large System Design) is Google's approach to SRE interviews. It requires concrete resource estimation.
NALSD differs from standard system design:
- Estimate actual numbers (QPS, storage, bandwidth)
- Calculate resource requirements (cores, RAM, disk I/O)
- Consider operational aspects (deployment, monitoring)
Example: Image sharing at K QPS
- Storage: K × KB avg × sec ≈ TB/day
- Bandwidth: K × KB = GB/sec
Interview tip: Practice back-of-envelope calculations. Interviewers want to see your estimation process, not perfect numbers.