File server system having tiered storage including solid-state drive primary storage and magnetic disk drive secondary storage

A file server system having solid-state drive primary storage and magnetic disk drive secondary storage aggressively moves newly created files from the primary storage to selected file systems in the secondary storage to match expected access patterns upon the files to different configurations of the file systems and for load balancing upon the file systems in the secondary storage. Upon read access to a file that has been moved to the secondary storage, or upon migration of a newly created file that was read in primary storage after creation, a corresponding stub file containing file mapping metadata is created in the primary storage. The file mapping metadata in the stub file maps the extent of the file to logical storage addresses in the secondary storage.