Efficient data access is one of the key factors for having a high performance data processing pipeline. Determining the layout of data values in the filesystem often has fundamental impacts on the performance of data access. In this talk, we will show insights on how data layout affects the performance of data access. We will first explain how modern columnar file formats like Parquet and ORC work and explain how to use them efficiently to store data values. Then, we will present our best practice on how to store datasets, including guidelines on choosing partitioning columns and deciding how to bucket a table.