Massive DW and Scalability
Scalability is the ability of a system to maintain its level of performance when the size of input grows.
When the size of input in DWs grows, DWs must be able to handle the number of users and the complexity of their queries.
Wal-Mart use hundreds of terabytes of data to study sales trends and other tasks.
US Defence use 5 petabyte DW to maintain the medical records of its 9 million personnel.
Good scalability of DW means that queries and other data access functions will grow (ideally) linearly with the size of the DW.