A sound understanding of storage scalability is really important if you intend to interview for a senior backend engineer or a senior infrastructure engineer role. 
We try to walk you through some of these problems here to set a tone around how to approach these problems. Do note that no design is correct or wrong. There are just good designs and bad designs which heavily depend on the use case. 
Hence, it is extremely important to clarify the requirements for the problem asked. We discuss this in more detail in later slides.