Cisco has just been awarded a U.S. patent, which shows that virtualization now applies as much to storage as it does to central computing resources. For that matter, virtualization is also being applied to I/O and memory resources. In practical terms, the patent, filed in 2005 but just granted last month, seems to relate to technology that appears in Cisco's SAN Fabric Switches, which incorporate virtual fabric support.
The patent itself, Number 7,581,056, is entitled "Load balancing using distributed front end and back end virtualization engines." Here's the top-level description, from the patent document:
"With the emergence of intelligent storage area networks, virtualization is being moved to the network. In some examples, fibre channel switches in a storage area network perform functions associated with mirroring and striping in a manner transparent to the hosts and end devices. However, mechanisms for efficiently and effectively configuring virtualization mechanisms are limited in storage area networks."
Here's a more nuts-and-bolts explanation of how it works:
"The virtualization engine includes a front end virtualization engine and a back end virtualization engine cluster. The front end virtualization engine is configured to receive an input/output (I/O) request from a host. The back end virtualization engine cluster includes multiple back end virtualization engines. One of the back end virtualization engines is selected to perform a virtual to physical lookup for the I/O request to allow forwarding of the I/O request to a selected target.
In another embodiment, a technique for performing network virtualization is provided. An input/output (I/O) request is received from a host at a front end virtualization engine. A back end virtualization engine is selected from a back end virtualization engine cluster. The back end virtualization engine is selected to perform a virtual to physical lookup for the I/O request to allow forwarding of the I/O request to a selected target."
Here's a flow diagram from the patent, putting this in visual terms:
Flow chart from Cisco's SAN virtualization patent. (Click picture to enlarge, and to see one additional chart.)
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I should point out that this whole load-balancing concept isn't spanking brand new. What I find interesting, as regards virtualization, is how all the technology threads that have been developed, tested, and deployed over the past few years are staring to jell into a field that's becoming more mature and developing best practices.
I should also note that patents take a very long time to work their way through the system. This one was filed in May 11, 2005 and was only recently granted on August 25, 2009. This means that by the time the USPTO gives its stamp of approval, the technology has been in the field a while.
For example, SAN virtualization is available in Cisco's MDS 9000 Series Multilayer SAN Switches. I grabbed some quick boilerplate by going to the white paper describing Cisco's MDS 9100 Series SAN Fabric Switches, which is the line aimed at the SMB market. (There are also 9200 and 9500 Series SKUs.) The document notes that "Cisco's virtual SAN (VSAN) technology virtualizes the SAN switch when bridging servers with storage. VSANs create logical SANs that emulate the physical infrastructure to provide flexibility in deployment and consolidation."
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