The usual way to incorporate tertiary storage is to extend the file system.
Small frequently used files remain on magnetic disk, while large and old
files that are not actively used are archived to the jukebox. some file-archiving
systems, the directory entry for the file continues to exist, but the contents of
the file no longer occupy space in secondary storage. If an application tries to
open the file, the system call is suspended until the file contents can
be staged in from tertiary storage. the contents are again available from
magnetic disk, the open() operation returns control to the application, which
proceeds to use the disk-resident copy of the data