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Downsides to Virtualization

First, increased network complexityaffects performance. Aside from merely increasing the number of network devices, virtualizationadds tiers to the switching fabric, increasing latency, power consumption and managementcomplexity.

Second, the consolidation of virtual machines on physical servers affects switching scalabilityand performance. As dual-processor servers with six-, eight- and even 10-core CPUs becomecommon, consolidation ratios will climb. Currently, a hypervisor virtual switch with a workloadof 10 to 15 VMs per system extracts a modest overhead of about 10% to 15%, but thatfigure that will undoubtedly increase when handling scores of VMs.

The third challenge is that software switching complicates management and security. Network monitoring, management, traffic reporting and security tools use standard protocols operating on physical ports, but as more traffic is switched within the hypervisor, these tools lose visibility into a significant amount of network activity. Some vendors make their monitoringand analysis software available on VMs to regain visibility, but these are proprietary solutions that typically support only one or two hypervisor vendors, and usually come with additional license costs.

Fourth, the ability to seamlessly and transparently move VMs from one physical server to another complicates management and security. Such dynamic movement of application workloads becomes a headache when keeping network policies aligned with applications.

Fifth, virtualization exacerbates demands for shared storage, due to the inherent need to decouple OS images, applications and data from the underlying server hardware.

-  Analyt i c s . Informat ionWeek. com

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