Первые впечатления тестеров:

Server density, availability and deployment all look impressive—and are head and shoulders over competitors, whether open source or from Microsoft.

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There was an impressive fault tolerance demonstration given during the announcement presentation: An instance of a Blackberry Enterprise Server was running on a blade that was unceremoniously removed from its chassis. The application continued to serve up e-mail even as vSphere automatically created a new lockstep guest to maintain the fault tolerant configuration.

Подробнее про VMware Fault Tolerance здесь http://www.vmware.com/products/fault-tolerance/, здесь http://www.vmware.com/files/pdf/resources/ft_virtualization_wp.pdf и здесь http://www.vsphere.ru/2009/04/vmware-fault-tolerance-preview/ 

eWEEK Labs’ First Take on VMware vSphere 4: Impressive