The other 2 areas sharing that file, would need to be assigned contiguous block numbers in the file. This could be done with a backup-restore, but it would also be doable with an unload-reload. The backup-restore would be easier and quicker.
The process using backup-restore would be: 1. Make the areas to be processed unavailable for update under the central version. (If re-using some of the existing files, take the area offline to the central version.) 2. Backup the areas using the AREA option of the BACKUP utility statement and the old DMCL. 3. Change the definition of the areas by excluding all files associated with the areas being changed and re-assigning the pages of the area to the new file blocks. 4. Generate, punch and link all DMCLs that contain the segment with which the areas are associated. 5. Allocate and format the new database file using the new DMCL. This step will change the file block assignment, so that the areas are assigned contiguous block numbers in the file. 6. Restore the areas using the AREA option of the RESTORE utility statement and the new DMCL. 7. Make the new DMCLs and the new files available to the runtime environment.