[lug] Backup comparison: rdiff-backup and rsync snapshots

[Sean Reifschneider]

On Wed, Dec 21, 2005 at 12:34:41AM -0700, Daniel Webb wrote:
>I'm curious as to the relative merits of rdiff-backup vs. rsync snapshots
>(http://www.mikerubel.org/computers/rsync_snapshots/).

rdiff-backup saves file meta-data like ACLs and SELinux attributes.  Or it
will, at some point.  Apparently it's broken now.

rsync snapshots, if they're like what I'm familiar with (hard linking the
directory tree into a rotating set of other directories before/after
running the rsync), are nice because they play well with the file-system.
You can just "locate" or "find" or "cp" the files.

>Am I mistaken in
>thinking that the rsync snapshots method would be very inefficient if a small
>part of a large file (like revision control databases) changed regularly?

If you have huge files that have small changes, that will indeed be a
problem.  However, with quality 250GB drives being $120, who really cares?
We run rsync snapshot backups of something around 40 machines doing various
duty for ourselves and our clients and don't really have any concerns about
that.  Sure, the 2GB database files that have some regular changes hurt a
bit, but rotating old backups off saves the day.

>How
>much overhead is involved in all those hardlinks compared to rdiff-backup's
>metadata overhead?

Well, hardlinks are pretty cheap as far as a filesystem goes.  It's just
one more inode...

Thanks,
Sean
-- 
 Program *INTO* a language, not *IN* it.
                 -- David Gries
Sean Reifschneider, Member of Technical Staff <jafo at tummy.com>
tummy.com, ltd. - Linux Consulting since 1995: Ask me about High Availability