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Re: [virt-tools-list] cache write back & barriers



On Thu, Jun 13, 2013 at 10:47:32AM +0200, folkert wrote:
> Hi,
> 
> > > In virt-manager I saw that there's the option for cache writeback for
> > > storage devices.
> > > I'm wondering: does this also make kvm to ignore write barriers invoked
> > > by the virtual machine?
> > 
> > No, that would be unsafe.  When the guest issues a flush then QEMU will
> > ensure that data reaches the disk with -drive cache=writeback.
> 
> Aha so the writeback behaves like the consume harddisks with write-cache
> on them.
> In that case maybe an extra note could be added to the virt-manager
> (excellent software by the way!) that if the client vm supports
> barriers, that write-back in that case then is safe. Agree?

CCed virt-manager mailing list so they can see your request.

Stefan


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