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From: Andreas Dilger <adilger@clusterfs.com>
Date: Tue, 16 Jul 2002 13:49:29 -0600
To: linux-kernel@vger.kernel.org, Christoph Hellwig <hch@infradead.org>,
       Stelian Pop <stelian.pop@fr.alcove.com>, Sam Vilain <sam@vilain.net>,
       dax@gurulabs.com
Subject: Re: [ANNOUNCE] Ext3 vs Reiserfs benchmarks
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On Jul 16, 2002  21:38 +0200, Matthias Andree wrote:
> On Tue, 16 Jul 2002, Christoph Hellwig wrote:
> > On Tue, Jul 16, 2002 at 02:53:01PM +0200, Matthias Andree wrote:
> > > Not if some day somebody implements file system level snapshots for
> > > Linux. Until then, better have garbled file contents constrained to a
> > > file than random data as on-disk layout changes with hefty directory
> > > updates.
> > 
> > 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.

Luckily, there is already an interface which does this -
sync_supers_lockfs(), which the LVM code will use if it is patched in.

Cheers, Andreas
--
Andreas Dilger
http://www-mddsp.enel.ucalgary.ca/People/adilger/
http://sourceforge.net/projects/ext2resize/

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