Capturing the total amount of data stored can be challenging depending on what applications are in use and how users behave. Centralized application data and corporately hosted personal or shared directory data are generally easy to locate. However, if users are permitted to, or are in the habit of storing data locally, identifying and accounting for all user data can be tremendously challenging.
In order for management to answer this question, it will need to employ some sort of monitoring tool to detect and report on data stored on all disk arrays, servers, and workstations. A number of tools that can collect and report this data exist. A snap shot of meta data from all existing files provides a rudimentary core of information to analyze. However, in order to effectively manage data storage over time regular detailed reports are necessary.
Read the entire white paper - attached.