Networking and Power Priorities
IT managers should bear in mind that when designing the data center, networking and power trump server chip selection. That said, the recent advances in server CPU designs will affect IT managers' decisions with regard to server virtualization platforms.
IT managers will need to be mindful of new hardware components, including NICs and memory configurations, that will improve VM performance but will also drive up the initial hardware purchase price. Premium 8GB ECC (error-correcting code) DDR 3 (double data rate 3) DIMMs (dual in-line memory modules) are among the most expensive components needed to fully equip a physical server to take full advantage of the Nehalem-based processors.
Another concern is how the current hypervisor platforms will use the new CPU features while maintaining backward compatibility.
When running on an Intel-based server, VMware ESX 3.5 uses a baseline of features that correspond to the Intel Merom processor core to enable enhanced VMotion capabilities.
VMware, working with Intel, intercepts the CPUID and tells the operating system that it is working with a CPU that has the features of a Merom processor, which was released in 2006 and uses the previous-generation Intel Core microprocessor architecture. This is the trade-off to enable enhanced VMotion across older Intel processors and Nehalem-based processors that are in the same VMotion cluster.
Rich Brunner, chief platform architect in the CTO Office of VMware, indicated that while ESX 3.5 is limited to one mode of enhanced VMotion-where all processors are presented as having the Merom feature set-ESX 4.0, which is currently in beta, will have more flexibility.
ESX 4.0 will present the CPUID of the lowest supported processor in the VMotion cluster. For example, in a mix of Penryn- and Nehalem-based processors, Penryn would be used. Looking ahead, Brunner said it is likely that when Intel processors based on the successor to Nehalem-code-named Westmere-are available, this form of backward compatibility would be continued.