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

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Message-ID: <alpine.DEB.2.02.1303192102350.31505@nftneq.ynat.uz>
Date:	Tue, 19 Mar 2013 21:04:15 -0700 (PDT)
From:	David Lang <david@...g.hm>
To:	Martin Steigerwald <Martin@...htvoll.de>
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

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?

David Lang
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