Db2 catalog storage requirements
Estimated storage requirements for the Db2 catalog include space for the entire set of Db2 catalog data sets and their indexes.
Data sets for the Db2 catalog and directory are managed by Db2 and must be SMS-managed. The SMS environment that you use for Db2 catalog and directory data sets must be established before you begin installation or migration to Db2 12. The SMS environment must include a data class for allocating the data sets in extended format and using extended addressability. You are not required to convert existing Db2 catalog and directory data sets to the SMS environment before migrating to Db2 12. These data sets will be converted the next time that the related table space is reorganized.