Re: [Qemu-devel] [PATCH] Stop VM on ENOSPC error

[Daniel P. Berrange]

On Wed, Jan 14, 2009 at 04:46:17PM +0000, Jamie Lokier wrote:
> Daniel P. Berrange wrote:
> > Thus I'd suggest we need an async notification of this event,
> > and only enable this behaviour if the app controlling QEMU has
> > explicitly enabled this notification / feature.
> 
> I think the behaviour should always be enabled (unless explicitly
> disabled, but I'm not sure why you'd want to do that).
> 
> A corrupt VM with data loss sounds much worse than a stopped VM to me.

You're not corrupting data in current code - you're just unable to finish
new writes, because an IO failure is propagated back to the guest. If the
guest is properly checking for & handling I/O failures, it should be pretty
much OK once the host space problem is resolved - perhaps a reboot + journal
recovery. 

Older QEMU certainly had catastrophic data loss on ENOSPC due to not sending
any I/O errors back to the guest, so it thought its write had succeeded when
in fact it had been thrown away. Current QEMU is more careful about error
propagation now.

Daniel
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