The backuppc documentation (
http://backuppc.sourceforge.net/faq/BackupPC.html#archive_functions) suggests the following (below), which I followed. Works fine.
now I just have to tweak the scheduling to get it do to the archives once a week at a particular time to be able to take them off-site etc.
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Configuring an Archive Host
To create an Archive Host, add it to the hosts file just as any other host and call it a name that best describes the type of archive, e.g. ArchiveDLT
To tell BackupPC that the Host is for Archives, create a config.pl file in the Archive Hosts's pc directory, adding the following line:
$Conf{XferMethod} = 'archive';
To further customise the archive's parameters you can adding the changed parameters in the host's config.pl file. The parameters are explained in the config.pl file. Parameters may be fixed or the user can be allowed to change them (eg: output device).
The per-host archive command is $Conf{ArchiveClientCmd}. By default this invokes
__INSTALLDIR__/BackupPC_archiveHost
which you can copy and customize as necessary.
Starting an Archive
In the web interface, click on the Archive Host you wish to use. You will see a list of previous archives and a summary on each. By clicking the ``Start Archive'' button you are presented with the list of hosts and the approximate backup size (note this is raw size, not projected compressed size) Select the hosts you wish to archive and press the ``Archive Selected Hosts'' button.
The next screen allows you to adjust the parameters for this archive run. Press the ``Start the Archive'' to start archiving the selected hosts with the parameters displayed.