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Virtual I/O for storage networks

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Virtual I/O at the network adapter

I/O virtualization at the network adapter level, offered by companies like Brocade Communications Systems Inc., Emulex Corp. and QLogic Corp., requires fewer high-speed adapters be provisioned and shared across a larger number of virtual machines, yet still guarantees the correct service levels for mission-critical VM apps. For example, a 10 GigE network adapter that’s virtual I/O-capable has the ability to be either divided into multiple virtual adapters or to have its bandwidth allocated on a percentage basis to predetermined groups of VMs.

In that scenario, a single 10 GigE virtual card could be divided into 10 1 GigE virtual cards. One of these virtual cards could be dedicated to virtual machine migration activities, a few may be dedicated to specific VMs that need guaranteed performance levels and the remaining “cards” could be shared as a combined pool across all the remaining virtual machines.

Because this is all done in hardware, the burden on the

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virtualization hypervisor is significantly reduced, which should return CPU resources to the host. In other words, the CPU cores don’t need to be interrupted to manage I/O sharing. Not only does the virtual I/O itself allow for greater VM density, it returns the CPU horsepower to support that density.

Another feature that’s appearing on these virtual I/O cards is the ability to create a virtual switch on the card. This is valuable in virtualized server environments in particular and can greatly reduce network traffic flowing out of the server. With this capability, two VMs on the same host could communicate directly with each other (a very common requirement). Instead of this traffic going all the way out to the physical switch, the virtual switch isolates the local traffic inside the physical host. This again helps internal virtual machine performance and improves overall network efficiency.

Finally, network adapters that can provide I/O virtualization have the ability to virtualize the type of storage protocol used. For example, some of these cards support FC, FCoE, 10 Gbps Ethernet and iSCSI. A virtual I/O adapter should be able to reconfigure port usage on-the-fly without interrupting servers or virtual machines. Today, some adapters require a reboot, but that’s expected to change.

This was first published in March 2012

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