Re: Is continuous replication of state possible?

[Avery Pennarun <apenwarr@nit.ca>]

On Fri, Jan 07, 2005 at 03:34:09PM +0000, Ian Pratt wrote:

> > I've been playing around with Xen a couple of months now and I am very 
> > much impressed. I am particularly found of the "live migration" feature. 
> > I was wondering if it is possible to make a instance continuously 
> > replicate the state of another instance and then make the other instance 
> > run if the original instance fails.
> 
> Software-implemented hardware fault-tolerance is on the Xen
> research roadmap.
> 
> It basically just requires deterministic execution and event
> injection. Doing this for uniprocessor guests is fairly straight
> forward. Doing it for SMP guests (with decent performance) is
> going to be a huge challenge, as determinism is hard to achieve. We're
> looking in to it...

I gather that the request was not to keep both of them *executing* at once,
but to simply keep the memory image on the clone system "mostly" in sync at
all times, so the failover could happen faster.  This should be easier than
actually trying to execute the code deterministically.

Have fun,

Avery


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