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

[Zoltan Kiss <zoltan.kiss@xxxxxxxxxx>]

On 24/01/13 11:45, George Shuklin wrote:
> > > I expect the outage due to the proto-suspend is dwarfed by the outage
> > > caused by a backend going away for however long it takes to notice,
> > > rebuild, reset the hardware, etc etc.
> > Indeed, probably the backend restoration would take at least 5
> > seconds. Compared to that, the suspend-resume and the frontend device
> > reinit is much shorter.
> > Probably in storage driver domains it's better to suspend the guest
> > immediately when the backend is gone, as the guest can easily crash if
> > the block device is inaccessible for a long time. In case of network
> > access, this isn't such a big problem.
> Some notes about guest suspend during IO.
>
> I tested that way for storage reboot (pause all domains, reboot ISCSI
> storage and resume every domain). If pause is short (less that 2
> minutes), guest can survive. If pause is longer than 2 minutes, guests
> in state of waiting for io completion, detects IO timeout after
> resuming  and cause IO error on virtual block devices. (PV).
Good point! I haven't considered that even if the guest is paused, 
during coming back it will still notice that timers expired. I think the 
original idea came from Paul, CCing him to raise awareness about this 
problem.
Zoli


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