Bowie Bailey wrote at about 12:26:16 -0500 on Wednesday, February 18, 2009:
> John Goerzen wrote:
> > Hi,
> >
> > I've been reading docs on BackupPC and I have a few questions about
> > how it works.
> >
> > First off, I gather that it keeps a hardlinked pool of data, so
> > whenever a file changes on any host, on the backup device, it will be
> > hardlinked to a file containing the same data, regardless of the host
> > it came from, right?
>
> Right.
>
> > So, given that, I don't really understand why there is a distinction
> > between a full and an incremental backup. Shouldn't either one take
> > up the same amount of space? That is, if you've got few changes on
> > the client, then on the server you're mostly just hardlinking things
> > anyway, right? So why is there a choice?
>
> The result is basically the same, the difference is in implementation.
> A full backup will compare the contents of every file on the system to
> see if anything has changed. An incremental will only check files whose
> change date has been updated since the last backup.
>
> I believe one of the main incremental backup issues is that they do not
> detect deleted files. Incremental backups are also usually MUCH faster
> than full backups. For example, one of my backups takes about 600
> minutes for a full backup, but only 56 minutes for an incremental.
Deleted files are detected. The only issue is if an existing file changes but
the timestamp is pre-dated to before the last backup.
>
> > Secondly, I gather that BackupPC mangles filenames. That doesn't
> > bother me, but how is it possible to use rsync in an efficient way
> > with that? rsync wouldn't be able to match up client-side filenames
> > with the server-side names since the server names are different, so it
> > wouldn't do its efficient transfers. Either that or you're having to
> > create temporary directory trees on the server, which sounds
> > inefficient. Or am I missing something?
>
> BackupPC uses its own implementation of rsync which knows how to handle
> the filenames and compression used by BackupPC.
More specifically, it uses a perl library to interface directly with
the rsync protocol.
>
> --
> Bowie
>
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-OSBC tackles the biggest issue in open source: Open Sourcing the Enterprise
-Strategies to boost innovation and cut costs with open source participation
-Receive a $600 discount off the registration fee with the source code: SFAD
http://p.sf.net/sfu/XcvMzF8H
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