Re: Dump corrupts ext2?

[Richard Gooch]

Andreas Dilger writes:
> On Oct 10, 2001  19:11 -0400, Doug McNaught wrote:
> > Lew Wolfgang <[e-mail]> writes:
> > > 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'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).
> 
> In Linus kernels 2.4.11+ the block devices and filesystems all use
> the page cache, so no more coherency issues.

Um, I thought that there wasn't going to be coherency? For example, if
you open /dev/sda and /dev/sda1, they each have a separate cache. I
remember some debate about this, and Linus pointed out how hard it was
to make things coherent.

				Regards,

					Richard....
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