[CentOS] Rsync and differential Backups

Mon Nov 9 16:26:05 UTC 2015
Valeri Galtsev <galtsev at kicp.uchicago.edu>

On Mon, November 9, 2015 10:01 am, Alessandro Baggi wrote:
> Hi list,
> how to perform a differential backup using rsync?

Differential comes from real backup systems. Rsync is much simpler IMHO,
"-b" backup flag only keeps older version or deleted file/directory with
extra "~" (or whatever you define) in its name. Making rsync behaving as
full blown backup system is too time consuming. Much less time consuming
will be to just to install some backup software. Backuppc I would
recommend for simple case like I understand yours is. Bacula will be my
choice when I need enterprise level system.

Just my $0.02.


> On web there is a great confusion about diff backup concept when
> searched with rsync.
> Users says diff because it copy only differences. For me differential is
> backup from last full backup.
> Other users says that to perform a differential backup I must include in
> rsync command: --backup --backup-dir=/some/path but from manual page of
> rsync:
> #############
> --backup-dir=DIR
>                In combination with the --backup option, this tells rsync
> to store all backups in the specified directory on the receiving side.
> This can be used for incremental backups.  You can additionally specify
> a backup suffix
>                using the --suffix option (otherwise the files backed up
> in the specified directory will keep their original filenames).
> ....
> ###################
> Then at this point, I can perform a full backup copying base dir after
> last incremental. I can performa an incremental backup saving change on
> a specified destdir (using --backup-dir).
> How I can perform a diff backup?
> I know that rsync check differences using "the base dir". This dir have
> "the same content" of backupped source. To make incremental, this base
> is used.
> Supposing that I've 500 GB data on source. Make/sync the base-dir of
> 500GB.
> Running a full backup (the result file must be a fullbackup.tar.gz), at
> the end of the process I get a base-dir of 500GB and a .tar.gz of +/-
> 500GB compressed. Is correct make full backup, performing first an
> incremental backup on the base-dir and then compress it on a .tar.gz? Or
> is better resync all source in alternative destdir?
> In this example I've spent the double space for a full and a base-dir.
> 500GB Source vs 1TB for base-dir and a full.tar.gz. There is a way to
> performs other operation (incr and diff) without using the base and save
> disk space?
> Thanks in advance.
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Valeri Galtsev
Sr System Administrator
Department of Astronomy and Astrophysics
Kavli Institute for Cosmological Physics
University of Chicago
Phone: 773-702-4247