You have a system with 100k QPS. 50% are writes. Writes are 1KB. How much disk bandwidth do you need (ignoring WAL/replication overhead)?

To solve this, calculate the volume of write traffic: 100,000 total QPS $\times$ 50% write ratio = 50,000 writes per second. Since each write is 1 KB, the total bandwidth needed is $50,000 \times 1 \text{ KB} = 50,000 \text{ KB/s}$, or exactly 50 MB/s. While a single SSD can easily handle 50 MB/s of sequential traffic, real-world systems must also account for 'Write Amplification' (the extra writes performed by the database engine for logs and indexing) and replication overhead. In practice, this 50 MB/s of application data might result in 100-200 MB/s of actual physical disk activity.