On Fri, Dec 23, 2011 at 7:52 PM,  <hansbkk AT gmail DOT com> wrote:
>
>> The distinction is between the contents of the file and the directory
>> entries pointing to it.   The contents of hardlinked files are all the
>> same, but rsync doesn't know anything about the hashed filenames for
>> the pool links.   It strictly follows the directory tree established
>> by the last full run (by default).   The concept of incremental vs.
>> differential sort-of relates to the 'incremental level" setting that
>> permits the comparison to merge in previous incrementals back to the
>> last full, finding the latest version of each file .   That involves a
>> trade-off of more server side work traversing multiple directory trees
>> vs. likely transferring less changed data.
>
> Thanks Les. So my snip above does hold when trying to conserve
> bandwidth (say over a WAN), but at the potential cost of increasing
> the time the backup session requires. In a high-speed local
> environment, processing time can be reduced by always using
> "differential" between fulls (by not enabling the "incremental"
> option).
>
> This only becomes a question if I got it wrong 8-)

The more significant difference may be the wall-clock time time for a
full rsync run, which always does a full read of all the data on the
remote side for a block checksum comparison, and may need to
read/uncompress on the server side.   If that isn't an issue you can
just do frequent fulls and not worry about doing rsyncs against
incremental levels.   If it is an issue, or you want to use the least
bandwidth possible, then you might use incremental levels and less
frequent fulls.

-- 
   Les Mikesell
     lesmikesell AT gmail DOT com

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