Multigeneration File Systems

[Henry Spencer]

The only version-numbering file system I've ever heard of that actually
sounded good was the one CMU designed for their Spice project.  (Don't
know if it was/is implemented the way the tech report described it, but
that's another story.)  They took the view that (by default) once you
created a file, it was immutable -- any attempt to change it resulted
in creation of a new file, i.e. a new version number.  This was automatic
and inescapable, and applied to *all* attempts to change the file --
there was no way to alter an existing version at all.  The idea was that
old versions would be migrated, automatically and fairly quickly, out to
laser disk or some similar bulk-storage medium, cheap enough and big
enough that you could afford to save everything forever.
-- 
				Henry Spencer @ U of Toronto Zoology
				{allegra,ihnp4,linus,decvax}!utzoo!henry