Virtual I/O for storage networks


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Virtual I/O gateways. Virtual I/O gateways, offered by firms such as Virtensys Ltd. (Virtensys is being acquired by Micron Technology Inc.) and Xsigo Systems Inc., could be thought of as switch-like appliances into which storage and network interface cards are installed and then presented as shared resources to the network. When used in this manner, the data center is basically installing a private fabric for server communication. To some extent a virtual I/O gateway can be thought of as an extended bus architecture where a PCI Express (PCIe) type of connection is extended from the server to the I/O gateway, except that bus is sharable between hosts.

A card is installed in the server that connects to the I/O gateway. It may be a PCIe extension card, but some vendors use InfinBand adapters while others may use 10 Gbps Ethernet adapters. The objective is to install something in the server that’s relatively low cost yet high performance because it will be augmenting the PCI bus.

The key difference between virtual I/O gateways and virtual I/O on the network adapter is that the virtual I/O gateway can share a single interface card across multiple servers. This provides some significant advantages in connectivity and resource optimization.

Cards that go into the I/O gateway, depending on the vendor, are either proprietary cards or off-the-shelf PCIe cards. Proprietary cards usually have better multihost sharing capabilities built into them.

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Gateways that use off-the-shelf PCI cards may provide a greater sense of flexibility but are restricted to the sharing capabilities built into the modern day PCI card, which right now is limited.

Another benefit of virtual I/O gateways is protection from future upgrade requirements.

Because the card or software driver provided by the I/O gateway vendor becomes the common denominator in all servers, the ability to move between different network and storage protocols and technologies becomes very easy.

For example if the current storage system connects to the servers via Fibre Channel, a new iSCSI storage system would require that these hosts replace or add to their FC interface cards with Ethernet NICs. (The exception would be servers using the virtual I/O adapters described above.) With a virtual I/O gateway-type of configuration, the I/O gateway card installed on the server would remain the same and a shared iSCSI card would be installed into the gateway. This would let a single card in the host perform both functions. The only change required to the server would be to its software configuration -- there wouldn’t be a need to physically change interface cards in each host. This not only delivers the flexibility to move among network types and protocols, but requires less server downtime to make the changes.

This was first published in March 2012

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