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Date: Wed, 10 Oct 2001 17:38:11 -0700
From: Mike Fedyk <mfedyk@matchmail.com>
To: Doug McNaught <doug@wireboard.com>
Cc: Lew Wolfgang <wolfgang@sweet-haven.com>, linux-kernel@vger.kernel.org
Subject: Re: Dump corrupts ext2?
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	Lew Wolfgang <wolfgang@sweet-haven.com>,
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On Wed, Oct 10, 2001 at 07:11:43PM -0400, Doug McNaught wrote:
> Lew Wolfgang <wolfgang@sweet-haven.com> writes:
> 
> > Hi Folks,
> > 
> > I was looking for some scripts to backup ext2 partitions
> > to multiple CDR's when I stumbled onto "cdbackup" at
> > http://www.cableone.net/ccondit/cdbackup/.
> > 
> > Alas, there is a warning saying:
> > 
> > "WARNING! When using this program under Linux, be sure not to use
> >  dump with kernels in the 2.4.x series. Using dump on an ext2
> >  filesystem has a very high potential for causing filesystem
> >  corruption.  As of kernel version 2.4.5, this has not been
> >  resolved, and it may not be for some time."
> > 
> > I don't recall any problems like this, does anyone have
> > additional comments?
> 
> I'm pretty sure this is because dump reads the block device directly
> (which is cached in the buffer cache), while the file data for cached
> files lives in the page cache, and the two caches are no longer
> coherent (as of 2.4).
>

IIRC, 2.2 didn't have a coherent buffer and page cache also.

I.E. if you "cat /dev/hda > /dev/null" you wouldn't be able to expect any
speedup when reading through the mounted filesystem (except for meta-data?).

Am I wrong?  Has Linux ever had a coherent page and buffer cache?
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