Hi,
Adam Goryachev wrote on 2014-11-28 13:24:41 +1100 [Re: [BackupPC-users] Turning
an incremental backup into a full backup]:
> On 28/11/14 13:11, Bodo Eggert wrote:
> > Is there a way to create a full backup by joining an incremental backuop
> > and it's full backup?
short answer: no, and for a good reason.
> > I need to backup a remote system, and while differential backups are
> > possible (with increasing difficulty), a full backup would require moving
> > the backup system to the remote site.
As Adam has pointed out, this is not true for rsync(d). A full rsync(d) backup
might even use *less* bandwidth, as it always uses the most recent backup as a
reference. For incremental backups, this would only be the case if the
IncrLevel is increased for each and every backup.
For other XferMethods, you need to realize that incremental backups are
inexact. You miss all deletions of files (meaning your latest backup will
"contain" files deleted long since) as well as files appearing somewhere
with old timestamps (e.g. renamed files, files extracted from archives or
copied with timestamp preserving options active). Thus you *need* regular
full backups.
Even for rsync(d), incremental backups can conceivably miss changes in
files, though this is much less likely.
It is true that rsync(d) full backups may take far longer than corresponding
incremental backups would, but this doesn't change by moving the backup system
to the remote site.
> > For now, I'm increasing the IncrLevels settings, but this does not seem to
> > be a good way, it's just the least bad way I can see.
This probably doesn't scale well. Constructing a view of a high level
incremental backup requires the BackupPC server to do a lot of work, and
it has to do it for each new backup to construct the reference backup
(assuming rsync(d) as XferMethod, that is), as well as for browsing backups
or restoring (for any XferMethod). At which IncrLevel are you currently?
Aside from that, your incremental backups cannot expire as long as higher
level incremental backups depend on them. You would effectively be forced to
keep all data forever, and when you finally run out of space, there is no easy
way out, because you cannot delete any backup except the most recent one(s).
> Given that is the whole point of rsync (reduce
> data transferred between the source and destination at the cost of
> RAM/CPU/time).
Put differently, if you are bandwidth limited, you should be using rsync(d)
anyway.
> Can you provide some more detail on your requirements, or the problem,
> and current configuration?
Regards,
Holger
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