From owner-freebsd-fs@FreeBSD.ORG  Sat Apr  7 11:58:57 2007
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Date: Sat, 7 Apr 2007 06:58:55 -0500
From: Jim Rees <rees@umich.edu>
To: Mike Wolman <mike@nux.co.uk>
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	<20070407103057.P20396@nux.eros.office>
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Cc: freebsd-fs@FreeBSD.org, freebsd-questions@freebsd.org
Subject: Re: some thoughts about gmirror
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Mike Wolman wrote:

  if you were keeping track of the blocks which had changed
  then you do not need to generate this list and simply send over the
  changed blocks.

Unison keeps a list of files at each end and only exchanges block lists for
files that have changed.  I use it to sync 40GB (10K files) over a 1Mbps
link and it's very fast.  It also will do two-way sync.