[svlug] archival file system?

[Reg. Charney]

I am looking for an open-source archival file system. This type of file 
system looks like any other, but files are "aged" by activity. Older 
files are moved to "backing storage" but still appear as normal files 
for all intents. The only penalty paid is time. If you request a file 
that has not been accessed in a long time, bringing it into high speed 
storage may to some time. Please note, I am not asking about a backup 
system. Backups are a logically different beast - one meant to protect 
you from lost data. The archival system is meant to optimize use of 
limited high speed storage. (Think of the limited space in many 
notebooks.)  TIA.

Reg.