Re: "raid5: multiple 1 requests for sector ..."

[Steve Lord <lord@sgi.com>]

> XFS+RAID5...
> 
> Below, Neil Brown says, "If I were the author of the filesystem
> I would be worried."
> 
> Are the authors of the filesystem worried?  ;)


I responded to this when the original message went out, and no one 
followed up on my suggestions. I am currently on the other side of
the Pacific ocean and have too a heavy meeting schedule to get involved
in this right now, maybe Eric can dig out my original message to the
xfs list and resend it.

Steve

> 
> (I'm CCing this to both the linux-xfs and linux-raid lists; hope
> no-one minds...)
> 
> Andrew Klaassen
> 
> 
> On Fri, Aug 24, 2001 at 08:21:05PM +1000, 
> Neil Brown wrote:
> 
> > On Friday August 17, ak@dkp.com wrote:
> 
> > > kernel: raid5: multiple 1 requests for sector 32029440
> > ...
> > > kernel: raid5: multiple 1 requests for sector 40
> > > kernel: raid5: multiple 1 requests for sector 76260224
> > > (etc)
> 
> > On Friday August 24, eyal@eyal.emu.id.au wrote:
> 
> > > I noticed this message recently. What does it mean? Is is harmfull?
> > > 
> > > Running 2.4.9 with xfs.
> 
> > It means that while raid5 had an outstanding write request on a
> > particular sector, it received another write request for the same
> > sector.
> > 
> > It trys to do the right thing and write them both out in the order
> > that it received them, but it is a bit of a worry that any filesystem
> > would do this.  I'm guessing that Andrew is using XFS too.  Is that
> > right?
> > 
> > While raid5 tries to keep the requests in order, and I suspect other
> > drivers do to, I don't think that it is reasonable to assume that no
> > device driver will ever re-order two requests for the same sector.
> > If I were the author of the filesystem I would be worried.
> > 
> > NeilBrown