Hard links

Ben Escoto bescoto@stanford.edu
Wed, 13 Mar 2002 02:34:42 -0800

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>>>>> "ND" == Nick Duffek <nick@duffek.com>
>>>>> wrote the following on Tue, 12 Mar 2002 21:31:21 -0500 (EST)

  ND> My point was that if you planned to save space by using hard
  ND> links in rdiff-backup-data, then you'd be just one step along a
  ND> continuum of compression.  Each step on that continuum is a
  ND> superset of its predecessors, so if you opted for a later one,
  ND> then you wouldn't need to implement the earlier ones.

Ok, I get it.  I would add to your discussion that in general there is
a tradeoff between transparency and compression, and rdiff-backup
tries to pick a reasonable compromise.  Something like the extreme
compression point can be achieved (in theory) now by making a tar of
the entire filesystem, and then compressing that.  Filesystem wide
diffs could be made by using something like xdelta on two tars of the
filesystem (representing different times), and then those diffs could
be compressed.  In theory, this would catch all the redundancy you

    Conversely, you could pick a point of even more transparency at
the expense of disk space just by creating a new directory every time
you wanted a backup, and copying the whole source directory over.

Ben Escoto

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