Este excerto dos documentos deve ajudá-lo:
The directory $PGDATA/pg_tblspc contains symbolic links that point to each of the non-built-in tablespaces defined in the cluster. Although not recommended, it is possible to adjust the tablespace layout by hand by redefining these links. Two warnings: do not do so while the server is running; and after you restart the server, update the pg_tablespace catalog with the new locations. (If you do not, pg_dump will continue to output the old tablespace locations.)