Re: Dump corrupts ext2?

From: H. Peter Anvin (
Date: Wed Oct 10 2001 - 21:57:50 EST

Followup to: <>
By author: Andreas Dilger <>
In newsgroup:
> >
> > 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.

How do you find a random block in the page cache? Last my
understanding was that the page cache is organized by inode/offset,
which wouldn't lend itself to looking up a random hardware block.

(Not to mention the fact that the filesystem is perfectly allowed not
to present anything like a coherent state to the disk while mounted,
which means that even if you did a snapshot in time you're not
guaranteed to have anything functional. I understand this can be done
by sending a "quiet point" command to the filesystems, followed by an
LVM snapshot, but I doubt may people do that!


<> at work, <> in private!
"Unix gives you enough rope to shoot yourself in the foot."	<>
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