New servers usually mean Fibre Channel (FC) host bus adapters (HBAs) for SAN traffic and Ethernet cards for NAS traffic. But I/O virtualization, or virtual I/O, changes that assumption.

"Virtual I/O allows servers to connect to a multitude of different targets irrespective of the protocol," says Patrick Guay, senior VP of marketing at Voltaire, a provider of virtual I/O routers in Billerica, MA.

To accomplish this, the virtual I/O router performs a "network address translation [NAT]-like function," says Bill Erdman, director of marketing at Cisco Systems' Server Virtualization Business Unit. Cisco's SFS 3012 Multi-fabric Server Switch connects to servers using InfiniBand and then translates the InfiniBand protocol to the respective IP or FC storage protocol used by the storage array.

Cisco finds that virtual I/O offers organizations the following benefits:

• It creates a pool of physical HBAs and network interface cards (NICs) that may be shared between servers.
• It eliminates the need to install and cable HBAs and NICs for each server.
• It breaks the physical 1:1 relationship between the server and its HBAs and NICs by assigning them virtual worldwide names (WWNs) or IP addresses.
• Server identities are stored on storage fabric, not on local disk drives.
• Storage may be presented using CIFS, FC, iSCSI or NFS protocols.

Voltaire approaches deployments differently. For InfiniBand drivers on the servers, Voltaire relies on drivers provided by the OS vendors and leaves server-to-storage mapping to other products.

"We rely on VMware to do server virtualization and products like FalconStor Software to do storage virtualization," says Guay.

Implementing virtual I/O can require significant cost and effort. For environments new to InfiniBand, Cisco's SFS 3012 and Voltaire's Grid Director ISR 9288 virtual I/O routers require servers to connect using InfiniBand HBA cards that cost approximately $900 each. Storage arrays can use NAS (CIFS or NFS) or SAN (iSCSI or FC) protocols for connectivity, although each router requires the installation of a blade supporting IP or FC.

The major downside associated with virtual I/O is that its options for server connectivity are limited. Virtual I/O routers only support servers hosting Windows or Linux OSes that run on x86-compatible hardware platforms and use InfiniBand for network connectivity. These types of barriers lead Guay to view I/O virtualization as "part of the next-generation data center."

--Jerome M. Wendt