Oracle and DB2, Comparison and Compatibility/Storage Model
Earlier we introduced a general architecture for a relational database. The word database, however, is used to identify several different things: the Database Server, the Database instance and the user data held in the database. Technically the database is the collection of user data, control files and log files that are held on disk - the physical storage. Data can be stored in Linux file systems, Linux raw partitions and different types of RAID storage. Both Oracle and IBM recommend the use of Linux files systems. Apart from similarities in preference for physical storage the logical layout of the data is different, for example in Oracle both table and index data can reside in the same tablespace, but DB2 implements separate table and index spaces. This section extends the constructs introduced earlier by describing the actual physical organization of data on disk for each database, and then how this organization is manifest in Tables, Indexes and Data Types for each database.