Les Mikesell wrote at about 13:13:46 -0500 on Thursday, June 11, 2009:
 > Mirco Piccin wrote:
 > > 
 > >> Also, is each daily file completely distinct from the previous one or
 > >> is just incrementally changed? Because if it is just incrementally
 > >> changed you may want to first rsync against the previous day's backup
 > >> to reduce network bandwidth.
 > > 
 > > My BackupPC is running on a VIA processor, max MB/s : less than 5 :-(
 > > So, backup 840 GB each time is not the best solution ...
 > > (this is the reason i did not configure the backup as you suggest)
 > > 
 > > Anyway, each daily file is quite similar to the each other, so rsync
 > > (or custom script) should be the better way to to the job.
 > 
 > That won't help unless each file is named the same as the previous one. 
 > Perhaps you could smb-mount the share into the backuppc server and move 
 > the files around so you always have the newest file under the same name 
 > in a subdirectory of the share for the duration of the backup - then you 
 > could put it back if you want. That would let you use the 'some number 
 > of fulls only' approach I suggested earlier and also transfer less data 
 > (but the rsync CPU vs. network tradeoff may be a wash).
 > 
 > If you don't use some approach to just get one file in the directory per 
 > day, you will probably run out of space on your 2nd full when you 
 > transfer the current week's files before the previous full can be 
 > deleted.  Or are you doing this already?
 > 

I think Mirco was saying "so rsync (or custom script) should be the
better way to to the job." I assume that he would write a simple
script that would do something like:
1. Hard link the last file version to a file with the name of the
   current file in another temporary directory:
        ln <tempdir>/<last-file-name> <backupdir>/<current-file-name>


2. Rsync the current file relative to the last file in tempdir:
                rsync -a  --link-dest=<tempdir> <sourcedir>/<current-file-name> 
<backupdir>/<current-file-name> 

   If there are no changes then a hard link is created (which is
   equivalent to a hard link to <backupdir>/<last-file-name>). If you
   would prefer the file to be copied rather than hard-linked even if
   no changes, then use --compare-dest instead of link-dest.

   If there are changes, then rsync will use last-file-name as the
   basis for creating the new backup. i.e. it will *copy* the
   unchanged blocks locally from <tempdir>/<last-file-name> and only
   transfer the *changed* blocks over the network link. (correct me if
   I'm wrong here of course).

3. Remove the temporary link file
                rm <tempdir>/<last-file-name>

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