Testing Data Center Virtualization: Are you asking the right questions?

Data centers today are larger, faster and more complex than ever. New technologies such as virtualization, Fibre Channel over Ethernet and 40/100 Gigabit Ethernet aim to help organizations move multiple traffic types – data, storage, video, and voice – onto a single, converged core. Validation of all these new technologies through testing is a crucial part of the product development and deployment process.

Today, let’s look at testing virtualization. Testing virtual network devices and servers poses several interesting new questions:

How can a test instrument attach to a virtual network device?
Often one physical interface may handle traffic for dozens of Virtual Machine (VM) instances, making it difficult to isolate and measure the performance of each VM instance. What’s needed is to virtualize the capabilities of the test instrument. A virtual test instrument resides in software, and thus runs inside the physical machine hosting virtual network and server instances. From the standpoint of the virtual network device, a test port looks exactly the same as it would in the physical world.

Can test instruments on virtual machines be trusted?
One strategy to ensure measurements can be trusted is to implement the entire test instrument – including software-based emulation of hardware components – in software. This approach requires a far more rigorous approach to system design than does software-only tool design. But the benefit is clear: by emulating the entire test instrument in software, the instrument’s measurements are far less dependent on extraneous factors. Such an instrument will produce more meaningful measurements than software-only tools.

Do virtual and physical switches offer comparable performance?
Line-rate throughput and low latency and jitter have long been the hallmarks of physical Ethernet switches, but their virtual counterparts may not compare. Even if virtual switches will never handle loads as heavy as physical switches (a dubious assumption in these early days of virtual networking), it is still important to conduct stress tests to describe the limits of system performance. Industry-standard methodologies for assessing unicast and multicast performance in switches and routers still apply in the virtual world.

Does a virtual switch support the same protocols and functions as a physical switch?
A network manager can reasonably expect any modern Ethernet switch to support features such as Virtual LANs (VLANs), Access Control Lists (ACLs), and Internet Group Management Protocol (IGMP) for forwarding multicast traffic. These protocols (and often many others) are often included as part of physical switch performance testing and should also be included as well when testing virtual switches.

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