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Date: Thu, 4 Jul 2013 09:13:00 +0200
From: Stefan Hajnoczi <stefanha@redhat.com>
Message-ID: <20130704071300.GA2584@stefanha-thinkpad.redhat.com>
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Subject: Re: [Qemu-devel] [RFC V8 01/24] qcow2: Add journal specification.
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To: =?iso-8859-1?Q?Beno=EEt?= Canet <benoit.canet@irqsave.net>
Cc: kwolf@redhat.com, qemu-devel@nongnu.org

On Wed, Jul 03, 2013 at 02:53:27PM +0200, Beno=EEt Canet wrote:
> > By the way, I don't know much about journalling techniques.  So I'm
> > asking you these questions so that either you can answer them straigh=
t
> > away or because they might warrant a look at existing journal
> > implementations like:
>=20
> I tried to so something simple and performing for the deduplication usa=
ge.
>=20
> That explain that there is no concept of transaction and that the journ=
al's
> block are flushed asynchronously in order to have an high insertion rat=
e.
>=20
> I agree with your previous comment is more a log than a journal.

Simple is good.  Even for deduplication alone, I think data integrity is
critical - otherwise we risk stale dedup metadata pointing to clusters
that are unallocated or do not contain the right data.  So the journal
will probably need to follow techniques for commits/checksums.

Stefan