The Case For I/O Virtualization

Posted by David Hill
September 17, 2009

When the term "virtualization" is used, the implicit assumption is that we're talking about "server virtualization." But other types of virtualization exist, such as storage virtualization. And now I/O (input/output) virtualization is starting to encroach upon our consciousness.

Just what is I/O virtualization?  Answering that question requires a brief review of the role of I/O in a system. The job of a computer is to perform "data processing." A CPU processes data from its associated transient memory, but the data typically has to be acquired from storage somewhere, and a network is used to link the two. The movement of data is all about I/Os (inputs are reads from storage to a server and outputs are writes to storage).

To be clear, the use of network may be grandiose when using direct attached storage where a bus or I/O interconnect is sufficient rather than a LAN or SAN, but logically any connectivity is still part of a network.

Now if I/O needs to get in or out of the server chassis box in conjunction with an external network composed of such things as cables and switches, an I/O adapter is necessary to connect and translate network protocols to the CPU/memory complex of a server. If the network is a SAN, a Fibre Channel HBA (host bus adapter) may be the I/O adapter. Or, if the connection is to a LAN or WAN, an Ethernet NIC (network interface card) may be used. However, the I/O adapter is located within the server box.

What I/O virtualization does is move these adapters from the server box to a new box called an I/O virtualization switch box that is external to the server. VirtenSys is joining the I/O virtualization party (where NextIO has played for over a year) by providing such a switch. With the VirtenSys solution, a single PCIe cable connection is made between each physical server and the I/O virtualization switch. Each server no longer has a dedicated I/O adapter, but rather has virtual I/O connectivity through non-dedicated access to I/O adapter resources on the I/O virtualization switch.

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