[rdiff-backup-users] A "digest stand-in" Option?

[Kent Borg]

I just discovered rdiff-backup and it looks wonderful!  But I have the
inevitable new-user question.


  Is there (or could there easily be) a--for lack of a better
  name--"digest stand-in" option?  Let me explain.


Using this option a file (or likely a zillion files) in the
destination could be substituted with a digest (MD5, say).  If the
matching source file doesn't change the stand-in doesn't either.  If
the matching source file does change then the stand-in turns back into
a regular file that gets all its details recorded (including its
previously digested starting point).

Why is this interesting?  With this feature it would be possible to
backup an entire computer, OS and all, without having to get exclusion
details exactly right, yet collapse down most of those OS files to
little digests.  Candidates for collapsing would be everything after a
fresh OS install except /etc and /home.  For files that are better
recovered from installation CDs, why copy and haul them around?

Possible?  (Already in there?)


Thanks,

-kb