Snapshotting for rollback after updates was[ Re: Drawing lessons from fatal SELinux bug #1054350]

[Simo Sorce]

On Sat, 2014-01-25 at 17:54 -0700, Chris Murphy wrote:
> On Jan 25, 2014, at 4:12 PM, Adam Williamson <awilliam at redhat.com> wrote:
> > 
> > * Do an offline update that includes Foo v2.0
> > * Boot the updated system, run Foo, it migrates its configuration to
> > some new scheme
> > * Realize there was something wrong with the update, roll it back
> > * Run Foo again, find it doesn't work because it's been migrated to the
> > new config scheme which the old version of Foo doesn't work with
> 
> I would grumble, but a configuration file being updated and made
> incompatible with the prior version would be tolerated. Ideally the
> application makes an unmodified copy. If it doesn't, new school
> restore with --reflink from snapshot, regular cp if using LVM thinp
> snapshots, and old school just restore the file from a conventional
> backup. Not such a big deal.
> 
> If it's something far less throw away than configuration files being
> changed, it's a bit more complicated how badly and quickly the
> conversation degrades. But I can hardly recall a recent example of
> this happening. It's just not that common in my experience.

What about mail application change the format of the mail folders ?

It happens, and it is *not* data you want to risk throwing away. There
are many other examples like this especially on the server side.

Simo.

-- 
Simo Sorce * Red Hat, Inc * New York