[Discuss] When you omit rsync '--update' option

[bill at mills-curran.net (Bill Mills-Curran)]

At least for interactive use, I recommend a dry run first "-n".  Even
if you stop the dry run after a screenful, you have a sanity test that
you didn't screw up the command (source, target, etc).

On Thu, May 03, 2012 at 02:16:17AM -0400, Rich Braun wrote:
> Date: Thu, 3 May 2012 02:16:17 -0400
> From: Rich Braun <richb at pioneer.ci.net>
> To: "discuss at blu.org" <discuss at blu.org>
> Subject: [Discuss] When you omit rsync '--update' option
> 
> I suffered a data loss yesterday and can't think of any possible recovery
> mechanism.  Perhaps I haven't thought it through completely; at the very least
> I can warn others about the dangers of rsync...
> 
> Hindsight:  *always* use the --update (or -u) option to rsync.  I made the
> faulty assumption that older data would not overwrite newer data, by default;
> nope.  You have to specify this option.  I can't fathom *why* it's not the
> default, but...nope.
> 
> So, once you've done this and seen the program start clobbering your
> recently-updated files (in the midst of otherwise doing what I wanted, copying
> some other files that weren't yet in my active volume), what recovery methods
> (besides proper backups) could be attempted to un-do the nefarious action of
> the rsync?
> 
> As for my backups:  I'd configured the backup for this disk volume a few
> months ago but it was silently failing.  (Sound familiar?)  Hindsight:  one or
> two days after configuring any new backup, perform a manual test restore;
> don't wait a couple months because you *won't* notice the problem until--a
> data loss.
> 
> In the olden days we had really good versioning filesystems that provided
> assurance that unless you were running 99% full all the time, you could revert
> to an earlier copy of a file.  The Linux 'ext4' filesystem doesn't seem to
> have versioning, but maybe it's got some hidden recovery methods that I don't
> know about.  My file is small, about 15 megs, but represents a lot of manual
> effort that I dread repeating.
> 
> Suggestions?  Commiseration?  War stories about data losses you've suffered or
> witnessed?
> 
> -rich
> 
> 
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