Re: ext3 and Software RAID

From: Neil Brown (neilb@cse.unsw.edu.au)
Date: Sun Oct 08 2000 - 05:18:46 EST


On Saturday October 7, adilger@turbolinux.com wrote:
> Matt Stegman writes:
> > A few weeks ago Alan Cox mentioned, in reply to someone asking about
> > building an enourmous RAID array,
> >
> > "Right now 2.2 doesnt support journalling over software raid so that would
> > stop you using reiserfs and ext3."
> >
> > http://kernelnotes.org/lnxlists/linux-kernel/lk_0008_05/msg00009.html
> >
> > Is this still true? I was going to use 2.2.17, with ext3-0.0.3b, and Ingo
> > Molnar's 2.2.17 RAID patch:
>
> This was just discussed on l-k last week. Basically, no it still doesn't
> work (not for 2.2 at least). The problem is with RAID doing buffer cache
> snooping and causing data to be written out-of-order to disk (on 2.2).
> This is fixed in 2.4, but there _may_ still be a problem in 2.4 when
> rebuilding the array (on disk failure) in 2.4... I'm not too sure of
> the latter though...

Rebuild arrays, either after unclean shutdown or after disc failure,
is kept entirely inside the md driver in 2.4, so there cannot be (and
is not) any interaction between raid rebuild and the filesystem.

So when ext3 becomes available for 2.4, it would work just fine over
raid.

NeilBrown

>
> Cheers, Andreas
> --
> Andreas Dilger \ "If a man ate a pound of pasta and a pound of antipasto,
> \ would they cancel out, leaving him still hungry?"
> http://www-mddsp.enel.ucalgary.ca/People/adilger/ -- Dogbert
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