possibly new rsync trick: rotating snapshots

[Mike Rubel]

> In addition to the comments regarding NFS etc.  You will
> find that with cp -l permissions and ownership will not be
> accurately preserved in older snapshots if someone chmod or
> chowns files on the original.

Oh--Thank you, you're quite right, I missed that.  If you use rsync -a,
then rsync *will* change the ownership/permissions on the target file, but
will *not* first unlink it (I had been working on the assumption that
rsync always behaves as if it had a --remove-destination flag set, but it
looks like that only holds for data, not metadata).

* To summarize: if a file's permissions/ownerships are changed in place,
* then on the next snapshot the new permissions/ownerships will affect all
* previous snapshots, not just the most recent one.  This is a serious
* problem in my mind, and I apologize for missing it.

I'm looking into a workaround now; in the meantime, I posted an update at
the top of the page.

> I have a complete system for automated rotating backups that
> i was planning on announcing shortly (GPL).  I have been
> using it for about a month so far and am quite pleased.
> It is a little more complex than your approach and provides
> more flexible rotation schedules with automatic image
> (snapshot) expiration.
> 
> If anyone wishes to look at it or be an alpha test site
> a periodically updated snapshot of the development area can
> be found at http://www.pegasys.ws/dirvish.

Looks interesting!  I'd like to give it a try.

Mike