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Date: Tue, 16 Jul 2002 23:06:39 +0200
From: Matthias Andree <matthias.andree@stud.uni-dortmund.de>
To: linux-kernel@vger.kernel.org
Subject: Re: [ANNOUNCE] Ext3 vs Reiserfs benchmarks
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References: <20020716193831.GC22053@merlin.emma.line.org> <Pine.LNX.4.44.0207161408270.3452-100000@hawkeye.luckynet.adm>
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On Tue, 16 Jul 2002, Thunder from the hill wrote:

> Hi,
> 
> On Tue, 16 Jul 2002, Matthias Andree wrote:
> > > or the blockdevice-level snapshots already implemented in Linux..
> > 
> > That would require three atomic steps:
> > 
> > 1. mount read-only, flushing all pending updates
> > 2. take snapshot
> > 3. mount read-write
> > 
> > and then backup the snapshot. A snapshots of a live file system won't
> > do, it can be as inconsistent as it desires -- if your corrupt target is
> > moving or not, dumping it is not of much use.
> 
> Well, couldn't we just kindof lock the file system so that while backing 
> up no writes get through to the real filesystem? This will possibly 
> require a lot of memory (or another space to write to), but it might be 
> done?

But you would want to backup a consistent file system, so when entering
the freeze or snapshot mode, you must flush all pending data in such a
way that the snapshot is consistent (i. e. needs not fsck action
whatsoever).
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