Online disk space is a valuable, relatively expensive, and frequently
scarce resource that is often abused by users who squander it on large
quantities of inactive data.  Large inactive files should instead be
moved to cheaper and more abundantly available offline or near-line
storage. Users, however, are often reluctant to utilize offline storage
because it is difficult to use.  An extension to the UNIX operating
system that transparently migrates inactive data between online and
offline storage is examined, enhanced, and evaluated.