Abstract: A method for implementing staged database migration of a database includes implementing a first migration stage by expanding headers for one or more subfiles from a first file address format to a second file address format, wherein subsequent overflow blocks to be associated with said one or more subfiles are selectable from an address space corresponding to said second file address format. A second migration stage is implemented, including expanding file address references of one or more index files from the first file address format to the second address format. The file address references are located within logical records (LRECs) in the one or more index files, the file address references pointing to one or more of the subfiles.