linux-kernel - RE: Software raid0 will crash the file-system, when each disk is 5TB

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Message-ID: <659F626D666070439A4A5965CD6EBF406B348A@gazelle.ad.endace.com>
Date:	Thu, 17 May 2007 17:38:57 +1200
From:	"Jeff Zheng" <Jeff.Zheng@...ace.com>
To:	"Neil Brown" <neilb@...e.de>, <david@...g.hm>,
	"Michal Piotrowski" <michal.k.k.piotrowski@...il.com>,
	"Ingo Molnar" <mingo@...e.hu>, <linux-raid@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <linux-fsdevel@...r.kernel.org>
Subject: RE: Software raid0 will crash the file-system, when each disk is 5TB


Yeah, seems you've locked it down, :D. I've written 600GB of data now,
and anything is still fine.
Will let it run overnight, and fill the whole 11T. I'll post the result
tomorrow

Thanks a lot though.

Jeff 

> -----Original Message-----
> From: Neil Brown [mailto:neilb@...e.de] 
> Sent: Thursday, 17 May 2007 5:31 p.m.
> To: david@...g.hm; Jeff Zheng; Michal Piotrowski; Ingo 
> Molnar; linux-raid@...r.kernel.org; 
> linux-kernel@...r.kernel.org; linux-fsdevel@...r.kernel.org
> Subject: RE: Software raid0 will crash the file-system, when 
> each disk is 5TB
> 
> On Thursday May 17, neilb@...e.de wrote:
> > 
> > Uhm, I just noticed something.
> > 'chunk' is unsigned long, and when it gets shifted up, we 
> might lose 
> > bits.  That could still happen with the 4*2.75T arrangement, but is 
> > much more likely in the 2*5.5T arrangement.
> 
> Actually, it cannot be a problem with the 4*2.75T arrangement.
>   chuck << chunksize_bits
> 
> will not exceed the size of the underlying device *in*kilobytes*.
> In that case that is 0xAE9EC800 which will git in a 32bit long.
> We don't double it to make sectors until after we add
> zone->dev_offset, which is "sector_t" and so 64bit arithmetic is used.
> 
> So I'm quite certain this bug will cause exactly the problems 
> experienced!!
> 
> > 
> > Jeff, can you try this patch?
> 
> Don't bother about the other tests I mentioned, just try this one.
> Thanks.
> 
> NeilBrown
> 
> > Signed-off-by: Neil Brown <neilb@...e.de>
> > 
> > ### Diffstat output
> >  ./drivers/md/raid0.c |    2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff .prev/drivers/md/raid0.c ./drivers/md/raid0.c
> > --- .prev/drivers/md/raid0.c	2007-05-17 
> 10:33:30.000000000 +1000
> > +++ ./drivers/md/raid0.c	2007-05-17 15:02:15.000000000 +1000
> > @@ -475,7 +475,7 @@ static int raid0_make_request (request_q
> >  		x = block >> chunksize_bits;
> >  		tmp_dev = zone->dev[sector_div(x, zone->nb_dev)];
> >  	}
> > -	rsect = (((chunk << chunksize_bits) + zone->dev_offset)<<1)
> > +	rsect = ((((sector_t)chunk << chunksize_bits) + 
> > +zone->dev_offset)<<1)
> >  		+ sect_in_chunk;
> >   
> >  	bio->bi_bdev = tmp_dev->bdev;
> 
-
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