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What if, instead of installing separate network and storage adapters in every server, the PCIe bus adapters could be virtualized and shared across multiple servers? Consider the potential cost and power savings for NICs, host bus adapters (HBAs) and SAS/SATA disk controller cards that could be shared across a rack of servers. A rack full of servers could have only one cable for each server connecting it to a virtualized set of I/O adapters at the top of the rack. Then that top-of-rack unit could dynamically direct all LAN, SAN and DAS traffic to the appropriate location as needed, such as end-of-row switches for example, leaving the servers to focus on computing. This "rack-area network" (RAN) concept can allow an entire rack of servers to have some of the same benefits as blade servers, but without the limitations of a blade server chassis. The consolidation realized in this scenario would also mean that the size of the rack servers could be reduced to 1 rack unit (1U) or even one-half of a rack unit (1/2 U).

Consider the movement of a virtual machine (VM) from one physical server to another physical server. Typically, this requires a SAN, because SANs are separate from the physical server and can be accessed from any server, assuming all of the security, zoning and logical unit numbering (LUN) masking issues have been addressed. What if movement of virtual machines could be made to work with any storage, rather than requiring a SAN? I/O virtualization-capable adapters

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would run some of the hypervisor functions in hardware, offloading the host CPU and freeing up CPU resource that could be used to host additional virtual machines or applications.

I/O virtualization vs. other networking technologies

Ethernet Data Center Bridging (DCB) and Fibre Channel over Ethernet (FCoE) are a pair of technologies that are young, but slightly more mature than I/O virtualization in today's marketplace. Together, DCB and FCoE allow for hardware consolidation by combining lossless Ethernet with Fibre Channel at the switch and at the host adapter. This DCB/FCoE technology combination provides some of the same type of consolidation that I/O virtualization provides, but it's actually complementary to IOV. Because the DCB/FCoE converged adapters run on the PCI Express bus, they can be used in an I/O virtualization environment and, therefore, could be shared across multiple servers. The host adapters that support DCB and FCoE currently support or will soon support IOV technologies such as Single-Root IOV (SR-IOV). An IOV environment can communicate with existing Ethernet, Fibre Channel and DCB/FCoE switches using existing adapters and, as far as the host servers are concerned, they're connected directly to those switch environments.

InfiniBand is another high-speed, low-latency network technology that's typically used in compute cluster environments for server-to-server communication. InfiniBand provides faster speeds than Ethernet today. The newer InfiniBand host adapters, known as host channel adapters (HCAs), run on the PCI Express bus and can support I/O virtualization. In addition, some vendors are developing I/O virtualization solutions built around InfiniBand technology, using InfiniBand as the high-speed carrier for the IOV infrastructure.

This was first published in February 2010

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