One of the most common objections to systems virtualization is the perception that system performance will not be as “good” in a virtualized environment.  VMware solutions virtualize four key hardware resources: processing, memory, storage and network, using a best-of-breed hypervisor to allocate these resources dynamically to balance changing application needs.

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Performance Implications for CPUs
CPU virtualization adds varying amounts of overhead, depending on a number of different factors. For processor-intensive applications, any CPU virtualization overhead likely translates into a reduction in overall performance.

However, VMware solutions have the ability to balance processor loads in a highly efficient manner, and VMware virtual machines can fully leverage multi- cores and multi-processor configurations, making it possible to run processor-intensive workloads such as databases and e-mail servers on virtual machines without adversely affecting application performance.

Performance Implications for Memory (RAM)
Virtualization does not decrease the amount of RAM required to run an application and its host operating system, and like any software, the virtualization layer requires its own portion of RAM. As such, memory is often a limiting factor in determining the total number of virtual machines that you can consolidate on to a single physical server.

VMware technology adds very little memory overhead offering advanced memory management mechanisms such as RAM over-commitment and transparent page sharing that automatically expand or contract the amount of RAM allocated each virtual machine as application loads increase and decrease. This capability lets you achieve a higher level of server consolidation than is possible with traditional static virtual memory.

Performance Implications for Storage
Virtual machines run complete, unmodified operating systems and as such require several gigabytes (GB) of storage space to hold all applications, documents, device drivers and other data. When multiple virtual machines are consolidated on a single physical server, they can impact I/O performance with their combined file size and simultaneous need for rapid access to stored data.

VMware solutions help to improve I/O performance through the VMware vStorage VMFS, which provides virtual machines with simultaneous access to shared data stores. Centralized storage helps reduce latency and increase throughput, and provides the foundation for unique capabilities such as live migration and consolidated backup.

Performance Implications for Networking
Networking sizing and performance considerations in a virtual infrastructure are very similar to networking considerations in physical IT environments. In most cases, network throughput of virtualized workloads is comparable to the network throughput of the physical workloads.

VMware offers an ideal platform for secure, high-speed networking between virtual machines on a single physical server, supporting network topologies that normally depend on the use of additional hardware to provide security and isolation. You can also network virtual machines across physical servers with transparency and high throughput, as each virtual machine gets its own IP address and can utilize up to four virtual network interface cards (NICs).

VMware Performance and Scalability[1]
VMware sets the standard for virtualization performance. Reviewers can find detailed performance demonstrations and competitive performance comparisons in the Performance Section of the VMware website:
<a href="http://www.vmware.com/technology/performance/index.html">http://www.vmware.com/technology/performance/index.html</a>

The results clearly demonstrate that with VMware solutions, users can achieve high-performance throughput in a heavily virtualized environment, even as the number of total supported users and the number of virtual machines increases.

How fast can VMware go? 100,000 IOPS and more.  I/O is widely referred to as one of the most critical performance bottlenecks in virtual environments. Over the course of VMware ESX evolution, currently in its third generation, VMware has constantly improved the ability of its hypervisor to satisfy even the most I/O-intense applications.

A recent test conducted by VMware with EMC Midrange Partner Solution Engineering Team showed that a single VMware ESX host is capable of driving over 100,000 IOPS, maxing out the throughput of 500 disk drives in a SAN.

Test specs:
16 virtual machines running Windows 2003
3 EMC CLARiiON CX3-80 (500 disk, 77TB)
I/O-intensive workload (8k block size, 100% random, mixed read/write)

When do you need such throughput?
15,000 IOPS - 10 times more IOPS than the average DB
30,000 IOPS - Higher than the peak load of many databases
60,000 IOPS - Roughly 120,000 MS Exchange mailboxes
100,000 IOPS - Roughly 200,000 MS Exchange mailboxes or 85 average 4-way DBs

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[1] From VMware’s VI3 Reviewer’s Guide - <a href="http://www.vmware.com/files/pdf/vi3_competitive_reviewer_guide.pdf">http://www.vmware.com/files/pdf/vi3_competitive_reviewer_guide.pdf</a>