Gvirstor "newfs" problem - help needed

[Pawel Jakub Dawidek]

On Mon, Aug 13, 2007 at 02:12:50PM +0200, Ivan Voras wrote:
> Arne Wörner wrote:
> > Hi!
> > 
> > --- Ivan Voras <ivoras at fer.hr> wrote:
> >> cg 0: bad magic number
> >>
> > I know that message from my tests with graid5...
> > It was clearly caused by a bug in graid5, but I cannot remember when or why it
> > happened...
> > I would guess, it happened because of some cache or request-sorting
> > mismanagement (the write didnt take place but the read was executed; or the
> > second write took place before the first write)... Is that possible in
> > gvirstor? Does newfs create such a request-pattern (overlapping write requests
> > <-- would be a little bit astonishing)?
> > 
> > But I can definitely say, that it was a bug in graid5...
> 
> Thanks for replying! gvirstor doesn't reorder IO and i doesn't have a
> cache, so it's not that. I agree that it's almost certainly a bug in
> gvirstor.
> 
> The only "slightly unusual" thing newfs does is that it first writes a
> "big" block, then reads a smaller block from within the written big
> block and doesn't like what it gets. But this scenario is well tested by
> my test cases and I don't see why it fails for newfs.

Ivan, try to configure gvirstor on top of gnop. Modify gnop to log only
requests between 81920 and 147456 (81920 + 65536). Something like:

	if ((bp->bio_offset >= 81920 && bp->bio_offset < 147456) ||
	    (bp->bio_offset + bp->bio_length >= 81920 &&
	     bp->bio_offset + bp->bio_length < 147456)) {
		G_NOP_LOGREQ(bp, "Request.");
	}

Run newfs and watch which gvirstor I/O request triggers request into
this area - my guess is that gvirstor recalculates something incorrectly
and instead of writting somewhere else it writes into this very place.

-- 
Pawel Jakub Dawidek                       http://www.wheel.pl
pjd at FreeBSD.org                           http://www.FreeBSD.org
FreeBSD committer                         Am I Evil? Yes, I Am!
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