Any thought to making a file plugin that creates copy on write files? The operation would be something like a hardlink which is invisible to the user and broken as soon as either file is modified.
Files could be COWed by a flag on the cp command (or really, perhaps that should be the default behavior) or with a utility (perhaps run as a periodic script to locate duplicates and COW them. This would greatly speed up the process of copying files. The behavior on break could be to duplicate the whole cowed file on the first right, or allow a COWed file to have alternate choices for blocks. Files would remain cowed until decowed, which would likely be bad for performance (due to fragmentation of alternate versions causing gaps in sequential scans), so the repacker could be taught to decow files that have too many alternate blocks.
