  In order to accommodate the ever-growing data from various, possibly
independent, sources and the dynamic nature of data usage rates in practical
applications, modern cloud data storage systems are required to be scalable,
flexible, and heterogeneous. Codes with hierarchical locality have been
intensively studied due to their effectiveness in reducing the average reading
time in cloud storage. In this paper, we present the first codes with
hierarchical locality that achieve scalability and flexibility in heterogeneous
cloud storage using small field size. We propose a double-level construction
utilizing so-called Cauchy Reed-Solomon codes. We then develop a triple-level
construction based on this double-level code; this construction can be easily
generalized into any hierarchical structure with a greater number of layers
since it naturally achieves scalability in the cloud storage systems.
