This document discusses capacity planning for deploying MongoDB. It defines capacity planning as planning for requirements like availability, throughput, and responsiveness by determining necessary resources like CPU, memory, storage, and network capacity. It emphasizes starting capacity planning before launch to avoid downtime. Key aspects of capacity planning for MongoDB include estimating working memory set size, storage I/O needs based on data size and access patterns, using tools like IOStat and MongoDB Management Service for monitoring and automation, and conducting iterative testing and deployments. Failure occurs if planned resources cannot meet requirements.