Re: [Xen-API] [Xen-devel] driver domain crash and reconnect handling

[Zoltan Kiss <zoltan.kiss@xxxxxxxxxx>]

On 24/01/13 15:10, Andrew Cooper wrote:
> > If you would do a suspend, the frontend driver flush out disk IO
> > >operations before suspend reached, and therefore there won't be anything
> > >to timeout after resume. However, if the storage driver domain just
> > >crashed, I guess the guest would crash at suspend. Maybe we can try out
> > >something to save the the ring buffer, and replay them back once the
> > >backend come back (but before resuming the guest). But I'm not sure
> > >whether the guest would handle the timeouts after the resume first, or
> > >cancel them if the requests were succesfully responded.
> > >
> > >Zoli
> Perhaps I am making this harder, but might it be best to wait for a
> short while (15-30 seconds) for the device driver domain to come back,
> and if it takes longer than that, pause the VM.
>
> This way, if the driver domain is fast to come back, all the guest
> notices is transitorily blocked IO, and if the driver domain is too slow
> (but does come back), all the guest might notices is a pause.
>
> Ultimately, if the driver domain never comes back, then we are in a no
> worse position than currently.
As Paul mentioned, pausing doesn't cause the guest to reconnect to the 
new backend, so you would need a suspend/resume. But in George's case, 
where the driver domain remains the same, this can work.
However to avoid George's problem with timeouts, a reconnect should be 
necessary. As Ian mentioned, the guest will replay the ring and that 
might help to avoid the timouts to happen.
Zoli

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