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Re: xbd0: WARNING: cache flush not supported by backend

On Fri, Sep 24, 2010 at 05:39:56PM -0400, Thor Lancelot Simon wrote:
> On Fri, Sep 24, 2010 at 07:58:08PM +0200, Manuel Bouyer wrote:
> > 
> > I guess this is because you're using -o log on the filesystems ?
> > In order to work reliably, NetBSD needs to be able to flush the underlying's
> > disk cache. This needs support in the backed driver, but this was not
> > provisionned by the Xen peoples (I'm not sure how or if linux manages
> > to run reliably a journaled filesystem without it) so it's a NetBSD
> > extention to the Xen block device protocol.
> I have wondered about this.  Linux guests hosted on NetBSD dom0 complain
> that they cannot do flushes or write barriers.  Hosted on Linux Dom0,
> they work fine.
> So I have to conclude that we just implement cache flushes in a different
> way than they do, not that they don't implement them.  Why?

I guess this is something that showed up in a later version of Xen then.
When I wrote the cache flush I'm almost sure nothing related was
present in the public interface.

With what linux guest do you see this ? I'm not seeing any warning
with the linux guests I use (RHEL5 like)

Manuel Bouyer <bouyer%antioche.eu.org@localhost>
     NetBSD: 26 ans d'experience feront toujours la difference

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