Re: [Qemu-devel] KVM call agenda for October 25

[Anthony Liguori]

On 10/25/2011 08:18 AM, Dor Laor wrote:
> On 10/25/2011 03:05 PM, Anthony Liguori wrote:
> > On 10/25/2011 07:35 AM, Kevin Wolf wrote:
> > > Am 24.10.2011 13:35, schrieb Paolo Bonzini:
> > > > On 10/24/2011 01:04 PM, Juan Quintela wrote:
> > > > > Hi
> > > > >
> > > > > Please send in any agenda items you are interested in covering.
> > > >
> > > > - What's left to merge for 1.0.
> > >
> > > I would still like to cache the default cache mode (probably to
> > > cache=writeback). We don't allow guests to toggle WCE yet which Anthony
> > > would have liked to see before doing the change. Is it a strict
> > > requirement?
> >
> > I don't see a way around it. If the default mode is cache=writeback,
> > then we're open to data corruption in any guest where barrier=0. With
> > guest togglable WCE, it ends up being a guest configuration issue so we
> > can more or less defer responsibility.
> >
> > Do you think it's a good idea to change the default mode w/o guest WCE
> > toggle support? What's your view about older guests if we change the
> > default mode? What's your main motivation for wanting to change the
> > default mode?
> >
> > I'd be much more open to changing the default mode to cache=none FWIW
> > since the risk of data loss there is much, much lower.
>
> A bit related to this, it would be nice to mark a VM un-migratable if
> cache!=none. Juan reports that currently it such VMs are exposed to data
> integrity issues so we need to fail migrating them automatically.

That's not correct.  cache!=none is perfectly safe *if* you have coherent shared 
storage.

Regards,

Anthony Liguori

> > Regards,
> >
> > Anthony Liguori
> >
> > > Kevin