[email protected] wrote:

> I claim that it's not possible for a two servers to have the same state. 
> or at least not with acceptable performance.

A lot depends on how you achieve that "same state" condition.  If you've got 
shared storage, then you don't have to migrate the storage.  Even if you do 
have to migrate the storage, do your storage update requirements on a 
per-second basis overwhelm the bandwidth you've got to the hot-standby machine?

I mean, mainframes have been doing this sort of thing for twenty or thirty 
years.  You can have a bomb literally take out an entire datacenter, and the 
backup mainframe can take over without a noticeable hiccup.  This is because 
both machines are kept in lock-step synchronization, and nothing gets 
returned to the caller until the remote system has responded that the 
operation is complete.

Expensive, yes.  But certainly do-able.  And something that could be 
replicated by more modern systems.

-- 
Brad Knowles <[email protected]>
LinkedIn Profile: <http://tinyurl.com/y8kpxu>
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