Re: [BackupPC-users] When do files get re-transferred?

[Les M. <les...@gm...>]

On Sat, Dec 24, 2011 at 8:48 PM, Rahul Amaram <ra...@sy...> wrote:
>
> Generally when transferring data using rsync, it compares the remote
> files with the local files using some checksum algorithm and transfers
> it only when they are different. From what I know, comparison using the
> checksum uses only a fraction of the bandwidth required to transfer the
> whole file. So while Backuppc performs a full backup, does it compare it
> with the local file stored during previous full backup? Or just blindly
> copy the entire file.

Simple answer is that only the differences are transferred, even in full runs.

> Also, from your response, it seems that going with more frequent
> incremental backups is what you suggest. However is there any downside
> to this? For instance, let us say the full-backup is about 6 months old,
> and some file in it gets corrupted. Then will this be identified by the
> incremental backups?

Actually I recommend fairly frequent fulls, with the default weekly
being reasonable for most situations.   The details to consider if you
need additional tuning are that the comparison base defaults to the
last full, copying increasingly large differences with each subsequent
incremental. You can change it to merge previous incrementals for the
comparison with the $Conf{IncrLevels} setting.  Fulls take much longer
than incrementals to complete because they do a read and block
checksum comparison of all the data, but rsync does not use much
bandwidth for this.

-- 
   Les Mikesell
     les...@gm...