Re: [BackupPC-users] "Full" backup

[Holger P. <wb...@pa...>]

Hi,

Les Mikesell wrote on 2009-05-22 15:10:56 -0500 [Re: [BackupPC-users] "Full" backup]:
> Daniel Carrera wrote:
> > Hello,
> > 
> > If BackupPC uses hard links, what exactly makes a full backup different 
> > from an incremental backup? Is it just the --checksum flag for rsync?
> 
> It depends on the xfer method. [...] with rsync it sets the -i flag so
> the checksums are compared.

actually, it's -I (--ignore-times), not -i (--itemize-changes).

> There are two steps here - the transfer (which smb/tar would do but 
> rsync will realize it can skip) and the pooling with hard links.  Note 
> that for rsync to avoid the transfer, the same file with the same name 
> must appear in the reference backup of the same pc

And I apparently never tire of pointing it out: the reference backup for a
full rsync backup is the *previous backup of the host*, the reference backup
for an incremental rsync backup is the *previous backup of lower level* of the
host. Level 1 incrementals will re-transmit any changed files until the next
full backup (because they are relative to the previous full, not to each
other). The next full will not re-transmit these files (unless they have
changed once again). It doesn't need to, because it will check the contents
anyway, so starting from a more recent point cannot introduce any errors.

So, to sum it up, a full backup clears up any errors that may have been
introduced (unlikely with rsync, but possible) and gives a new reference point
for future backups.

Regards,
Holger