Redundant disk is used hold copies of the data for immediate use in case the original is damaged, so they represent double counting when it comes to what most users really mean when they inquire about database size. Freespace, which is available for workspace or to provide for future database growth. Freespace often has more to do with the amount of disk that was convenient or economical to acquire at the last purchase point than it does to any ordinary meaning of database size. Summary data, which consists of precomputed aggregates that are stored so that predictable queries can be serviced more rapidly. Depending on the product, these may or may not be visible to the end user.
Indexes are structures maintained by the database engine to speed access to the data.
Such structures are invisible to the end user or application, are created under DBA control, and are also a form of redundant data storage. User data, which represents the actual information content of the database. Examples would be base facts about customers, products, sales, stores, and so forth. In a relational database, these are the base tables. Now let's take a look at what real-life VLDBs look like in these terms.