linux-kernel - Re: Tux3 Report: Initial fsck has landed

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Message-Id: <201303201129.41996.Martin@lichtvoll.de>
Date:	Wed, 20 Mar 2013 11:29:41 +0100
From:	Martin Steigerwald <Martin@...htvoll.de>
To:	David Lang <david@...g.hm>
Cc:	tux3@...nq.net,
	Daniel Phillips <daniel.raymond.phillips@...il.com>,
	"Theodore Ts'o" <tytso@....edu>,
	"Darrick J. Wong" <darrick.wong@...cle.com>,
	linux-kernel@...r.kernel.org, tux3@...3.org,
	linux-fsdevel@...r.kernel.org
Subject: Re: Tux3 Report: Initial fsck has landed

Am Mittwoch, 20. März 2013 schrieb David Lang:
> On Wed, 20 Mar 2013, Martin Steigerwald wrote:
> > Am Dienstag, 29. Januar 2013 schrieb Daniel Phillips:
> >> On Mon, Jan 28, 2013 at 5:40 PM, Theodore Ts'o <tytso@....edu> wrote:
> >>> On Mon, Jan 28, 2013 at 04:20:11PM -0800, Darrick J. Wong wrote:
> >>>> On Mon, Jan 28, 2013 at 03:27:38PM -0800, David Lang wrote:
> >>>>> The situation I'm thinking of is when dealing with VMs, you make a
> >>>>> filesystem image once and clone it multiple times. Won't that end
> >>>>> up with the same UUID in the superblock?
> >>>> 
> >>>> Yes, but one ought to be able to change the UUID a la tune2fs
> >>>> -U.  Even still... so long as the VM images have a different UUID
> >>>> than the fs that they live on, it ought to be fine.
> >>> 
> >>> ... and this is something most system administrators should be
> >>> familiar with.  For example, it's one of those things that Norton
> >>> Ghost when makes file system image copes (the equivalent of "tune2fs
> >>> -U random /dev/XXX")
> >> 
> >> Hmm, maybe I missed something but it does not seem like a good idea
> >> to use the volume UID itself to generate unique-per-volume metadata
> >> hashes, if users expect to be able to change it. All the metadata
> >> hashes would need to be changed.
> > 
> > I believe that is what BTRFS is doing.
> > 
> > And yes, AFAIK there is no easy way to change the UUID of a BTRFS
> > filesystems after it was created.
> 
> In a world where systems are cloned, and many VMs are started from one
> master copy of a filesystem, a UUID is about as far from unique as
> anything you can generate.
> 
> BTRFS may have this problem, but why should Tux3 copy the problem?

I didn´t ask for copying that behavior. I just mentioned it :)

-- 
Martin 'Helios' Steigerwald - http://www.Lichtvoll.de
GPG: 03B0 0D6C 0040 0710 4AFA  B82F 991B EAAC A599 84C7
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