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In Pictures: Windows Server 8 - Ten features manag...
You can use a Hyper-V Replica in Windows Server 8 as a standby server in the event of a server crash or other catastrophe. Windows Server 8 will continuously sync the original server with the Hyper-V Replica, so you always have a virtual server backup that is current within 5 minutes of the original, and can be configured for automatic failover and failback.
In Pictures: Windows Server 8 - Ten features managers will love