Is there a file migration system?

[Ken Olum]

I'm looking for a system which does file migration in the style of various
operating systems like TOPS-20.  The idea is that you find files that
haven't been used in a long time and write the files on tape and replace
the disk file with a link of some sort.  Then when the user tries to use
the offline file they get an error about how the file is offline and can
request that it be retrieved.  Has anyone written anything like this?

					Ken