Linux file system that ages off older files when partition is full

There exist many HSM (Hierarchical Storage Management) systems, mainly aimed at SAN systems. These migrate files from faster disks, to slower disks, to tape as their last-access-time becomes older. You might like to seek out one of these, if you have a SAN. Most of the ones I know of are commercial licenses though, such as the IBM Tivoli HSM that we use. You might like to take a look at OHSM though.

If you just want to delete old files, then a simple cron job such as find /data -atime +30 -exec rm {} \; will delete files that have not been accessed in a certain amount of time (but make sure the filesystem is not mounted with the noatime option!) This would be highly risky, though, unless you had a good online backup system.