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Re: [Xen-devel] Is continuous replication of state possible?

To: Avery Pennarun <apenwarr@xxxxxx>
Subject: Re: [Xen-devel] Is continuous replication of state possible?
From: Ian Pratt <Ian.Pratt@xxxxxxxxxxxx>
Date: Fri, 07 Jan 2005 17:42:51 +0000
Cc: Ian Pratt <Ian.Pratt@xxxxxxxxxxxx>, Per Buer <perbu@xxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxxx, Ian.Pratt@xxxxxxxxxxxx
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> > 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.

It's not clear whether shipping checkpoints or just doing
deterministic execution will actually work best; that's why its
on the research roadmap. There are implementations in-progress of
both CoW checkpoints and deterministic execution.

Ian


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